As filed with the Securities and Exchange Commission on April 4, 2006

Registration No. 333-124858

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Post-Effective Amendment No. 1

to

Form S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Mariner Energy, Inc.

(Exact name of registrant as specified in its charter)

One Briar Lake Plaza, Suite 2000

2000 West Sam Houston Parkway South

Houston, Texas 77042

(713) 954-5500

(Address, including zip code, and telephone number,

including area code, of registrant’s principal executive offices)

Teresa Bushman

Vice President and General Counsel

Mariner Energy, Inc.

One Briar Lake Plaza, Suite 2000

2000 West Sam Houston Parkway South

Houston, Texas 77042

(713) 954-5505

(Name, address, including zip code, and telephone number,

including area code, of agent for service)

Copies to:

     Approximate date of commencement of proposed sale to the public: From time to time after the effective date of this registration statement.

     If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act, check the following box.    þ

     If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

     If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

     If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

     If delivery of the prospectus is expected to be made pursuant to Rule 434, please check the following box.    o

     The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

EXPLANATORY NOTE

     This Post-Effective Amendment No. 1 to the Registration Statement incorporates by reference the Registrant’s Annual Report on Form 10-K for the period ended December 31, 2005, as filed with the Securities and Exchange Commission on March 31, 2006, and the Registrant’s Current Reports on Forms 8-K/A and 8-K as filed with the Securities and Exchange Commission on March 31, 2006 and April 4, 2006, respectively.

SUBJECT TO COMPLETION

PRELIMINARY PROSPECTUS DATED APRIL 4, 2006

PROSPECTUS

33,348,130 Shares

Common Stock

         This prospectus relates to up to 33,348,130 shares of the common stock of Mariner Energy, Inc., which may be offered for sale by the selling stockholders named in this prospectus. The selling stockholders acquired the shares of common stock offered by this prospectus in private equity placements. We are registering the offer and sale of the shares of common stock to satisfy registration rights we have granted.

      We are not selling any shares of common stock under this prospectus and will not receive any proceeds from the sale of common stock by the selling stockholders. The shares of common stock to which this prospectus relates may be offered and sold from time to time directly from the selling stockholders or alternatively through underwriters or broker-dealers or agents. The shares of common stock may be sold in one or more transactions, at fixed prices, at prevailing market prices at the time of sale or at negotiated prices. Because all of the shares being offered under this prospectus are being offered by selling stockholders, we cannot currently determine the price or prices at which our shares of common stock may be sold under this prospectus. Shares of our common stock are listed on the New York Stock Exchange under the symbol “ME.” On March 31, 2006, the closing price of our common stock as reported on the New York Stock Exchange was $20.51 per share. Please read “Plan of Distribution.”

      Investing in our common stock involves risks. You should read the section entitled “Risk Factors” beginning on page 18 of our Annual Report on Form 10-K for the fiscal year ended December 31, 2005, which is incorporated by reference herein, for a discussion of certain risk factors that you should consider before investing in our common stock.

      You should rely only on the information contained in or incorporated by reference into this prospectus or any prospectus supplement or amendment. We have not authorized anyone to provide you with different information. We are not making an offer of these securities in any state where the offer is not permitted.

      Neither the Securities and Exchange Commission (the “SEC”) nor any state securities commission has approved or disapproved of these securities or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is                           , 2006.

TABLE OF CONTENTS

WHERE YOU CAN FIND MORE INFORMATION

      We have filed with the SEC, under the Securities Act of 1933, as amended (the “Securities Act”), a registration statement on Form S-1 with respect to the common stock offered by this prospectus. This prospectus, which constitutes part of the registration statement, does not contain all the information set forth in the registration statement or the exhibits and schedules which are part of the registration statement, portions of which are omitted as permitted by the rules and regulations of the SEC. Statements made in this prospectus regarding the contents of any contract or other documents are summaries of the material terms of the contract or document. You should not assume that the information contained in this prospectus is accurate as of any date other than the date on the front of this document. Our business, financial condition, results of operations and prospects may have changed since that date. Any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference. With respect to each contract or document filed as an exhibit to the registration statement, reference is made to the corresponding exhibit. For further information pertaining to us and to the common stock offered by this prospectus, reference is made to the registration statement, including the exhibits and schedules thereto, copies of which may be inspected without charge at the public reference facilities of the SEC at 100 F Street, N.E., Washington, D.C. 20549. Copies of all or any portion of the registration statement may be obtained from the SEC at prescribed rates. Information on the public reference facilities may be obtained by calling the SEC at 1-800-SEC-0330. In addition, the SEC maintains a web site that contains reports, proxy and information statements and other information that is filed electronically with the SEC. The web site can be accessed at www.sec.gov.

      Upon completion of this offering, we will be required to comply with the informational requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and, accordingly, will file current reports on Form 8-K, quarterly reports on Form 10-Q, annual reports on Form 10-K, proxy statements and other information with the SEC. Those reports, proxy statements and other information will be available for inspection and copying at the public reference facilities and internet site of the SEC referred to above.

      We have elected to “incorporate by reference” certain information into this prospectus, which means we can disclose important information to you by referring you to another document filed with the SEC. The information incorporated by reference is deemed to be part of this prospectus. Please read “Incorporation by Reference.” You should only rely on the information contained in this prospectus and incorporated by reference in it. We have not authorized anyone to provide you with any additional information.

INCORPORATION BY REFERENCE

      We are incorporating by reference into this prospectus the following documents filed with the SEC (excluding any portions of such documents that have been “furnished” but not “filed” for purposes of the Securities Exchange Act of 1934, as amended):

      Any statement contained in this prospectus or a document incorporated by reference in this prospectus will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or in any other subsequently filed document that is incorporated by reference in this prospectus modifies or supersedes the statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

      The documents incorporated by reference in this prospectus are available from us upon request. We will provide a copy of any and all of the information that is incorporated by reference in this prospectus to any person, without charge, upon written or oral request. Requests for such copies should be directed to the following:

Mariner Energy, Inc.

One BriarLake Plaza, Suite 2000

2000 West Sam Houston Parkway South

Houston, Texas 77042

Telephone Number: (713) 954-5500

Attention: General Counsel

																			Production for
			Estimated Proved																Year Ended
			Reserve Quantities																December 31,
																			2005
							Natural								Total
			Oil				Gas				Total				Net				(Natural Gas
Geographic Area			(MMbbls)				(Bcf)				(Bcfe)				Acreage				Equivalent (Bcfe))
West Texas Permian Basin				16.7				105.5				205.5				31,199				6.6
Gulf of Mexico Deepwater(1)				4.7				83.2				111.1				185,271				11.8
Gulf of Mexico Shelf(2)				0.3				19.0				21.0				124,180				10.7
	Total			21.7				207.7				337.6				340,650				29.1
Proved Developed Reserves				9.6				110.0				167.4

(1)		Deepwater refers to water depths greater than 1,300 feet (the approximate depth of deepwater designation for royalty purposes by the U.S. Minerals Management Service).
(2)		Shelf refers to water depths less than 1,300 feet and includes an insignificant amount of Gulf Coast onshore properties.

			Pro Forma																Pro Forma
			Estimated Proved																Production for
			Reserve Quantities																Year Ended
																			December 31,
															Pro Forma				2005
							Natural								Total
			Oil				Gas				Total				Net				(Natural Gas
Geographic Area			(MMbbls)				(Bcf)				(Bcfe)				Acreage				Equivalent (Bcfe))
West Texas Permian Basin				16.7				105.5				205.5				31,199				6.6
Gulf of Mexico Deepwater(1)				4.8				95.7				124.5				241,320				14.0
Gulf of Mexico Shelf(2)				12.7				237.6				313.7				652,086				74.3
	Total			34.2				438.8				643.7				924,605				94.9
Proved Developed Reserves				18.4				252.1				362.3

(1)		Deepwater refers to water depths greater than 1,300 feet (the approximate depth of deepwater designation for royalty purposes by the U.S. Minerals Management Service).
(2)		Shelf refers to water depths less than 1,300 feet and includes an insignificant amount of Gulf Coast onshore properties.

Common stock offered by selling stockholders		33,348,130 shares.
Use of proceeds		We will not receive any proceeds from the sale of the shares of common stock by the selling stockholders.
Listing		Our common stock is listed on the New York Stock Exchange under the symbol “ME.”
Common stock split		Unless specifically indicated or the context requires otherwise, the share and per share information of this offering gives effect to a 21,556.61594 to 1 stock split, which was effected on March 3, 2005.
Dividend Policy		We do not expect to pay dividends in the near future.

	•	Oil and natural gas prices are volatile, and a decline in oil and natural gas prices would affect significantly our financial results and impede our growth.
	•	Reserve estimates depend on many assumptions that may turn out to be inaccurate. Any material inaccuracies in these reserve estimates or underlying assumptions will affect materially the quantities and present value of our reserves.
	•	Unless we replace our oil and natural gas reserves, our reserves and production will decline.
	•	Relatively short production periods or reserve life for Gulf of Mexico properties subject us to higher reserve replacement needs and may impair our ability to replace production during periods of low oil and natural gas prices.

CAUTIONARY STATEMENT CONCERNING FORWARD-LOOKING STATEMENTS

      Various statements contained in or incorporated by reference into this prospectus, including those that express a belief, expectation, or intention, as well as those that are not statements of historical fact, are forward-looking statements. The forward-looking statements may include projections and estimates concerning the timing and success of specific projects and our future production, revenues, income and capital spending. Our forward-looking statements are generally accompanied by words such as “estimate,” “project,” “predict,” “believe,” “expect,” “anticipate,” “potential,” “plan,” “goal” or other words that convey the uncertainty of future events or outcomes. The forward-looking statements in this prospectus speak only as of the date of this prospectus; we disclaim any obligation to update these statements unless required by securities law, and we caution you not to rely on them unduly. We have based these forward-looking statements on our current expectations and assumptions about future events. While our management considers these expectations and assumptions to be reasonable, they are inherently subject to significant business, economic, competitive, regulatory and other risks, contingencies and uncertainties, most of which are difficult to predict and many of which are beyond our control. We disclose important factors that could cause our actual results to differ materially from our expectations under “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” incorporated by reference into this prospectus, and elsewhere in this prospectus. These risks, contingencies and uncertainties relate to, among other matters, the following:

USE OF PROCEEDS

      We will not receive any of the proceeds from the sale of the shares of common stock offered by this prospectus. Any proceeds from the sale of the shares offered by this prospectus will be received by the selling stockholders.

DILUTION

      Our net tangible book value as of December 31, 2005 was $5.99 per share of common stock. Net tangible book value per share is determined by dividing our tangible net worth (tangible assets less total liabilities) by the 35,615,400 shares of our common stock that were outstanding on December 31, 2005. Investors who purchase our common stock in this offering may pay a price per share that exceeds the net tangible book value per share of our common stock. If you purchase our common stock from the selling stockholders identified in this prospectus, you will experience immediate dilution of $11.76 in the net tangible book value per share of our common stock assuming a sale price of $17.75 per share, representing the December 23, 2005 price at which the shares traded in the PORTAL Market^®. The following table illustrates the per share dilution to new investors purchasing shares from the selling stockholders identified in this prospectus:

      The foregoing discussion and table are based upon the number of shares actually issued and outstanding as of December 31, 2005. As of December 31, 2005, we had 809,000 stock options outstanding at an average exercise price of approximately $14.00 per share, none of which were vested as of December 31, 2005. To the extent the market value of our shares is greater than $14.00 per share and any of these outstanding options are exercised, there may be further dilution to new investors.

DIVIDEND POLICY

      We do not expect to pay dividends in the near future. Our credit facility contains restrictions on the payment of dividends to stockholders.

SELLING STOCKHOLDERS

      This prospectus covers shares currently owned by an affiliate of our former sole stockholder as well as shares sold in our recent private equity placement. Some of the shares sold in the private equity placement were sold directly to “accredited investors” as defined by Rule 501(a) under the Securities Act pursuant to an exemption from registration provided in Regulation D, Rule 506 under Section 4(2) of the Securities Act. In addition, we and our former sole stockholder sold shares to FBR, who acted as initial purchaser and sole placement agent in the offering. FBR sold the shares it purchased from us and our sole stockholder in transactions exempt from the registration requirements of the Securities Act to persons that it reasonably believed were “qualified institutional buyers,” as defined by Rule 144A under the Securities Act or to non-U.S. persons pursuant to Regulation S under the Securities Act. An affiliate of our former sole stockholder, the selling stockholders who purchased shares from us or FBR in the private equity placement and their transferees, pledgees, donees, assignees or successors, may from time to time offer and sell under this prospectus any or all of the shares listed opposite each of their names below. Some of the shares reflected in the following table were issued as restricted stock to our employees pursuant to our Equity Participation Plan.

      The following table sets forth information about the number of shares owned by each selling stockholder that may be offered from time to time under this prospectus. Certain selling stockholders may be deemed to be “underwriters” as defined in the Securities Act. Any profits realized by the selling stockholder may be deemed to be underwriting commissions.

      The table below has been prepared based upon the information furnished to us by the selling stockholders as of March 17, 2006. The selling stockholders identified below may have sold, transferred or otherwise disposed of some or all of their shares since the date on which the information in the following table is presented in transactions exempt from or not subject to the registration requirements of the Securities Act. Information concerning the selling stockholders may change from time to time and, if necessary, we will supplement this prospectus accordingly. We cannot give an estimate as to the amount of shares of common stock that will be held by the selling stockholders upon termination of this offering because the selling stockholders may offer some or all of their common stock under the offering contemplated by this prospectus. The total amount of shares that may be sold hereunder will not exceed the number of shares offered hereby. Please read “Plan of Distribution.”

      Except as noted below, to our knowledge, none of the selling stockholders has, or has had within the past three years, any position, office or other material relationship with us or any of our predecessors or affiliates, other than their ownership of shares described below.

PLAN OF DISTRIBUTION

      We are registering the common stock covered by this prospectus to permit selling stockholders to conduct public secondary trading of these shares from time to time after the date of this prospectus. Under the Registration Rights Agreement we entered into with selling stockholders, we agreed to, among other things, bear all expenses, other than brokers’ or underwriters’ discounts and commissions, in connection with the registration and sale of the common stock covered by this prospectus. We will not receive any of the proceeds of the sale of the common stock offered by this prospectus. The aggregate proceeds to the selling stockholders from the sale of the common stock will be the purchase price of the common stock less any discounts and commissions. A selling stockholder reserves the right to accept and, together with their agents, to reject, any proposed purchases of common stock to be made directly or through agents.

      The common stock offered by this prospectus may be sold from time to time to purchasers:

      The selling stockholders and any underwriters, broker-dealers or agents who participate in the sale or distribution of the common stock may be deemed to be “underwriters” within the meaning of the Securities Act. The selling stockholders identified as registered broker-dealers in the selling stockholders table above (under “Selling Stockholders”) are deemed to be underwriters with respect to securities sold by them pursuant to this prospectus. As a result, any profits on the sale of the common stock by such selling stockholders and any discounts, commissions or agent’s commissions or concessions received by any such broker-dealer or agents may be deemed to be underwriting discounts and commissions under the Securities Act. Selling stockholders who are deemed to be “underwriters” within the meaning of Section 2(11) of the Securities Act will be subject to prospectus delivery requirements of the Securities Act. Underwriters are subject to certain statutory liabilities, including, but not limited to, Sections 11, 12 and 17 of the Securities Act.

      The common stock may be sold in one or more transactions at:

      These sales may be effected in one or more transactions:

      These transactions may include block transactions or crosses. Crosses are transactions in which the same broker acts as an agent on both sides of the trade.

      In connection with the sales of the common stock, the selling stockholders may enter into hedging transactions with broker-dealers or other financial institutions which in turn may:

      To our knowledge, there are currently no plans, arrangements or understandings between any selling stockholders and any underwriter, broker-dealer or agent regarding the sale of the common stock by the selling stockholders. The maximum amount of compensation to be received by any participating NASD member will not exceed 8% of the total proceeds of the offering.

      Our common stock is listed on the New York Stock Exchange under the symbol “ME.” However, we can give no assurances as to the development of liquidity or any trading market for the common stock.

      There can be no assurance that any selling stockholder will sell any or all of the common stock under this prospectus. Further, we cannot assure you that any such selling stockholder will not transfer, devise or gift the common stock by other means not described in this prospectus. In addition, any common stock covered by this prospectus that qualifies for sale under Rule 144 or Rule 144A of the Securities Act may be sold under Rule 144 or Rule 144A rather than under this prospectus. The common stock covered by this prospectus may also be sold to non-U.S. persons outside the U.S. in accordance with Regulation S under the Securities Act rather than under this prospectus. The common stock may be sold in some states only through registered or licensed brokers or dealers. In addition, in some states the common stock may not be sold unless it has been registered or qualified for sale or an exemption from registration or qualification is available and complied with.

      The selling stockholders and any other person participating in the sale of the common stock will be subject to the Exchange Act. The Exchange Act rules include, without limitation, Regulation M, which may limit the timing of purchases and sales of any of the common stock by the selling stockholders and any other such person. In addition, Regulation M may restrict the ability of any person engaged in the distribution of the common stock to engage in market-making activities with respect to the particular common stock being distributed. This may affect the marketability of the common stock and the ability of any person or entity to engage in market-making activities with respect to the common stock.

      We have agreed to indemnify the selling stockholders against certain liabilities, including liabilities under the Securities Act.

      We have agreed to pay substantially all of the expenses incidental to the registration, offering and sale of the common stock to the public, including the payment of federal securities law and state blue sky registration fees, except that we will not bear any underwriting discounts or commissions or transfer taxes relating to the sale of shares of our common stock.

DESCRIPTION OF CAPITAL STOCK

      The authorized capital stock of Mariner consists of 180 million shares of common stock, par value of $.0001 each, and 20 million shares of preferred stock, par value of $.0001 each.

      The following summary of the capital stock and certificate of incorporation and bylaws of Mariner does not purport to be complete and is qualified in its entirety by reference to the provisions of applicable law and to our certificate of incorporation and bylaws.

Common Stock

      As of March 17, 2006, there were a total of 86,100,994 shares of our common stock issued and outstanding, including 1,803,614 shares of restricted stock issued to executive officers pursuant to our Equity Participation Plan as amended, that are expected to vest on May 31, 2006. Our board of directors has reserved 6,500,000 shares for issuance as restricted stock or upon the exercise of stock options granted or that may be granted under our Amended and Restated Stock Incentive Plan, as amended, approximately 867,584 of which, as of March 17, 2006, had been granted as restricted stock or were subject to options granted to certain of our employees and directors. In addition, our board of directors has reserved 156,626 shares of common stock for issuance upon exercise of options granted or to be granted to certain former employees of Forest or Forest Energy Resources that became or will become employees of Mariner Energy Resources, Inc. in connection with the Forest Energy Resources merger. These options are governed by nonstatutory stock option agreements with Mariner Energy, Inc. and are not covered by its Amended and Restated Stock Incentive Plan, as amended. Holders of our common or restricted stock are entitled to one vote for each share held on all matters submitted to a vote of stockholders and do not have cumulative voting rights. Holders of a majority of the shares of our common stock entitled to vote in any election of directors may elect all of the directors standing for election. Except as otherwise provided in our certificate of incorporation and bylaws or required by law, all matters to be voted on by our stockholders must be approved by a majority of the votes entitled to be cast by all shares of common stock. Our certificate of incorporation requires approval of 80% of the shares entitled to vote for the removal of a director or to adopt, repeal or amend certain provisions in our certificate of incorporation and bylaws. See “— Anti-Takeover Effects of Provisions of Delaware Law, Our Certificate of Incorporation and Bylaws”.

      Holders of our common stock are entitled to receive proportionately any dividends if and when such dividends are declared by our board of directors, subject to any preferential dividend rights of outstanding preferred stock. Upon liquidation, dissolution or winding up of our company, the holders of our common stock are entitled to receive ratably our net assets available after the payment of all debts and other liabilities and subject to the prior rights of any outstanding preferred stock. Holders of our common stock have no preemptive, subscription, redemption or conversion rights. The rights, preferences and privileges of holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that we may designate and issue in the future.

Liability and Indemnification of Officers and Directors

      Our certificate of incorporation provides that our directors will not be personally liable to us or our stockholders for monetary damages for breach of fiduciary duty as a director, except for liability (1) for any breach of a director’s duty of loyalty to us or our stockholders, (2) for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law, (3) under Section 174 of the Delaware General Corporation Law, or (4) for any transaction from which the director derives an improper personal benefit. If the Delaware General Corporation Law is amended to authorize the further elimination or limitation of directors’ liability, then the liability of our directors will automatically be limited to the fullest extent provided by law. Our certificate of incorporation and bylaws also contain provisions to indemnify our directors and officers to the fullest extent permitted by the Delaware General Corporation Law. These provisions may have the practical effect in certain cases of eliminating the ability of stockholders to collect monetary damages from our directors and officers. We believe that these contractual agreements and the provisions in our certificate of incorporation and bylaws are necessary to attract and retain qualified persons as directors and officers.

Preferred Stock

      Our certificate of incorporation authorizes the issuance of up to 20 million shares of preferred stock and no preferred shares are outstanding. The preferred stock may carry such relative rights, preferences and designations as may be determined by our board of directors in its sole discretion upon the issuance of any shares of preferred stock. The shares of preferred stock could be issued from time to time by the board of directors in its sole discretion (without further approval or authorization by the stockholders), in one or more series, each of which series could have any particular distinctive designations as well as relative rights and preferences as determined by the board of directors. The existence of authorized but unissued shares of preferred stock could have anti-takeover effects because we could issue preferred stock with special dividend or voting rights that could discourage potential bidders.

      Approval by the stockholders of the authorization of the preferred stock gave the board of directors the ability, without stockholder approval, to issue these shares with rights and preferences determined by the board of directors in the future. As a result, Mariner may issue shares of preferred stock that have dividend, voting and other rights superior to those of the common stock, or that convert into shares of common stock, without the approval of the holders of common stock. This could result in the dilution of the voting rights, ownership and liquidation value of current stockholders.

Anti-Takeover Effects of Provisions of Delaware Law, Our Certificate of Incorporation and Bylaws

      Our certificate of incorporation and bylaws contain the following additional provisions, some of which are intended to enhance the likelihood of continuity and stability in the composition of our board of directors and in the policies formulated by our board of directors. In addition, some provisions of the Delaware General Corporation Law, if applicable to us, may hinder or delay an attempted takeover without prior approval of our board of directors. Provisions of the Delaware General Corporation Law and of our certificate of incorporation and bylaws could discourage attempts to acquire us or remove incumbent management even if some or a majority of our stockholders believe this action is in their best interest. These provisions could, therefore, prevent stockholders from receiving a premium over the market price for the shares of common stock they hold.

      Our certificate of incorporation provides that our board of directors will be divided into three classes of directors, with the classes to be as nearly equal in number as possible. As a result, approximately one-third of our board of directors will be elected each year. The classification of directors will have the effect of making it more difficult for stockholders to change the composition of our board of directors. Our certificate of incorporation and bylaws provide that the number of directors will be fixed from time to time exclusively pursuant to a resolution adopted by the board of directors.

      Our certificate of incorporation provides that vacancies and newly created directorships resulting from any increase in the authorized number of directors may be filled by the affirmative vote of a majority of our directors then in office, though less than a quorum. Each director will hold office until his or her successor is elected and qualified, or until the director’s earlier death, resignation, retirement or removal from office. Any director may resign at any time upon written notice to us. Our certificate of incorporation provides, in accordance with Delaware General Corporation Law, that the stockholders may remove directors only by a super-majority vote and for cause. We believe that the removal of directors by the stockholders only for cause, together with the classification of the board of directors, will promote continuity and stability in our management and policies and that this continuity and stability will facilitate long-range planning.

      Our certificate of incorporation precludes stockholders from initiating or effecting any action by written consent and thereby taking actions opposed by the board of directors.

      Our bylaws provide that special meetings of our stockholders may be called at any time only by the board of directors acting pursuant to a resolution adopted by the board and not the stockholders.

      Our bylaws provide that stockholders seeking to bring business before or to nominate candidates for election as directors at an annual meeting of stockholders must provide timely notice of their proposal in writing to the corporate secretary. With respect to the nomination of directors, to be timely, a stockholder’s notice must be delivered to or mailed and received at our principal executive offices (i) with respect to an election of directors to be held at the annual meeting of stockholders, not later than 120 days prior to the anniversary date of the proxy statement for the immediately preceding annual meeting of the stockholders and (ii) with respect to an election of directors to be held at a special meeting of stockholders, not later than the close of business on the 10th day following the day on which such notice of the date of the special meeting was first mailed to Mariner’s stockholders or public disclosure of the date of the special meeting was first made, whichever first occurs. With respect to other business to be brought before a meeting of stockholders, to be timely, a stockholder’s notice must be delivered to or mailed and received at our principal executive offices not less than 120 days prior to the anniversary date of the proxy statement for the immediately preceding annual meeting of the stockholders. Our bylaws also specify requirements as to the form and content of a stockholder’s notice. These provisions may preclude stockholders from bringing matters before an annual meeting of stockholders or from making nominations for directors at an annual meeting of stockholders or may discourage or defer a potential acquirer from conducting a solicitation of proxies to elect its own slate of directors or otherwise attempting to obtain control of us.

      The Delaware General Corporation Law provides that stockholders are not entitled to the right to cumulate votes in the election of directors unless our certificate of incorporation provides otherwise. Under cumulative voting, a majority stockholder holding a sufficient percentage of a class of shares may be able to ensure the election of one or more directors. Our certificate of incorporation expressly precludes cumulative voting.

      Our certificate of incorporation provides that the authorized but unissued shares of preferred stock are available for future issuance without stockholder approval and does not preclude the future issuance without stockholder approval of the authorized but unissued shares of our common stock. These additional shares may be utilized for a variety of corporate purposes, including future public offerings to raise additional capital, corporate acquisitions and employee benefit plans. The existence of authorized but unissued shares of common stock and preferred stock could make it more difficult or discourage an attempt to obtain control of Mariner by means of a proxy contest, tender offer, merger or otherwise.

      As permitted by Section 122(17) of the Delaware General Corporation Law, our certificate of incorporation provides that Mariner renounces any interest or expectancy in any business opportunity or transaction in which any of our original institutional investors or their affiliates participate or seek to participate. Nothing contained in our certificate of incorporation, however, is intended to change any obligation or duty that a director may have with respect to confidential information of Mariner or prohibit Mariner from pursuing any corporate opportunity.

      Pursuant to the Delaware General Corporation Law and our certificate of incorporation, certain anti-takeover provisions of our certificate of incorporation may not be repealed or amended, in whole or in part, without the approval of at least 80% of the outstanding stock entitled to vote.

      Our certificate of incorporation permits our board of directors to adopt, amend and repeal our bylaws. Our certificate of incorporation also provides that our bylaws can be amended by the affirmative vote of the holders of at least 80% of the voting power of the outstanding shares of our common stock.

      We are subject to Section 203 of the Delaware General Corporation Law, an anti-takeover law. In general, this section prevents certain Delaware companies under certain circumstances, from engaging in a “business combination” with (1) a stockholder who owns 15% or more of our outstanding voting stock (otherwise known as an “interested stockholder”); (2) an affiliate of an interested stockholder; or (3) an associate of an interested stockholder, for three years following the date that the stockholder became an “interested stockholder.” A “business combination” includes a merger or sale of 10% or more of our assets.

Transfer Agent and Registrar

      Our transfer agent and registrar for our common stock is The Continental Stock Transfer & Trust Company.

REGISTRATION RIGHTS

      We entered into a registration rights agreement in connection with our private equity placement in March 2005. In the registration rights agreement we agreed, for the benefit of FBR, the purchasers of our common stock in the private equity placement, MEI Acquisitions Holdings, LLC and holders of the common stock issued under our Equity Participation Plan, as amended, or Amended and Restated Stock Incentive Plan, as amended, that we will, at our expense:

      We have filed the registration statement of which this prospectus is a part to satisfy our obligations under the registration rights agreement with respect to common stock issued in the private equity placement and under our Equity Participation Plan, as amended. We have filed a Form S-8 registration statement to cover shares of our common stock issuable under our Amended and Restated Stock Incentive Plan, as amended.

      Notwithstanding the foregoing, we will be permitted, under limited circumstances, to suspend the use, from time to time, of the shelf registration statement of which this is a part (and therefore suspend sales under the registration statement) for certain periods, referred to as “blackout periods,” if, among other things, any of the following occurs:

      The cumulative blackout periods in any 12 month period commencing on the closing of the private equity placement may not exceed an aggregate of 90 days and furthermore may not exceed 60 days in any 90-day period, except as a result of a review of any post-effective amendment by the SEC prior to declaring it effective; provided we have used all commercially reasonable efforts to cause such post-effective amendment to be declared effective.

      In addition to this limited ability to suspend use of the shelf registration statement, until we are eligible to incorporate by reference into the registration statement our periodic and current reports, which will not occur until at least one year following the end of the month in which the registration statement of which this prospectus is a part is declared effective, we will be required to amend or supplement the shelf registration statement to include our quarterly and annual financial information and other developments material to us. Therefore, sales under the shelf registration statement will be suspended until the amendment or supplement, as the case may be, is filed and effective.

      A holder that sells our common stock pursuant to the shelf registration statement will be required to be named as a selling stockholder in this prospectus, as it may be amended or supplemented from time to time, and to deliver a prospectus to purchasers, will be subject to certain of the civil liability provisions under the Securities Act in connection with such sales and will be bound by the provisions of the registration rights agreement that are applicable to such holder (including certain indemnification rights and obligations). In addition, each holder of our common stock must deliver information to be used in connection with the shelf registration statement in order to have such holder’s shares of our common stock included in the shelf registration statement.

      Each holder will be deemed to have agreed that, upon receipt of notice of the occurrence of any event which makes a statement in the prospectus which is a part of the shelf registration statement untrue in any material respect or which requires the making of any changes in such prospectus in order to make the statements therein not misleading, or of certain other events specified in the registration rights agreement, such holder will suspend the sale of our common stock pursuant to such prospectus until we have amended or supplemented such prospectus to correct such misstatement or omission and have furnished copies of such amended or supplemented prospectus to such holder or we have given notice that the sale of the common stock may be resumed.

      We have agreed to use our commercially reasonable efforts to satisfy the criteria for listing and list or include (if we meet the criteria for listing on such exchange or market) our common stock on the New York Stock Exchange, American Stock Exchange or The Nasdaq National Market (as soon as practicable, including seeking to cure in our listing or inclusion application any deficiencies cited by the exchange or market), and thereafter maintain the listing on such exchange.

EXPERTS

      The consolidated financial statements of Mariner Energy, Inc. as of December 31, 2005, December 31, 2004 (Post-2004 Merger), December 31, 2003 (Pre-2004 Merger) and for the period from January 1, 2004 through March 2, 2004 (Pre-2004 Merger), for the period from March 3, 2004 through December 31, 2004 (Post-2004 Merger), and for each of the two years in the period ended December 31, 2003 incorporated by reference into this prospectus from Mariner’s Annual Report on Form 10-K for the fiscal year ended December 31, 2005, have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report (which report expresses an unqualified opinion and includes explanatory paragraphs relating to the adoption in 2003 of SFAS No. 143, “Accounting for Asset Retirement Obligations” and the merger in 2004 of the Mariner’s parent) which is incorporated herein by reference, and has been so incorporated in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.

      The statements of revenues and direct operating expenses of the Forest Gulf of Mexico operations for each of the years in the three-year period ended December 31, 2005 have been incorporated by reference herein in reliance upon the report of KPMG LLP, independent registered public accounting firm, incorporated by reference into this prospectus, and upon the authority of such firm as experts in accounting and auditing.

      The information included in this prospectus regarding estimated quantities of proved reserves, the future net revenues from those reserves and their present value is based, in part, on estimates of the proved reserves and present values of proved reserves of Mariner as of December 31, 2003, 2004 and 2005 and prepared by or derived from estimates prepared by Ryder Scott Company, L.P., independent petroleum engineers. These estimates are included in this prospectus in reliance upon the authority of the firm as experts in these matters.

LEGAL MATTERS

      The validity of the shares of Mariner common stock offered pursuant to this prospectus will be passed upon by Baker Botts L.L.P.

GLOSSARY OF OIL AND NATURAL GAS TERMS

      The following is a description of the meanings of some of the oil and gas industry terms used in this prospectus. The definitions of proved developed reserves, proved reserves and proved undeveloped reserves have been abbreviated from the applicable definitions contained in Rule 4-10(a)(2-4) of Regulation S-X. The entire definitions of those terms can be viewed on the website at http://www.sec.gov/divisions/corpfin/forms/regsx.htm#gas.

      3-D seismic. (Three-Dimensional Seismic Data) Geophysical data that depicts the subsurface strata in three dimensions. 3-D seismic data typically provides a more detailed and accurate interpretation of the subsurface strata than two dimensional seismic data.

      Appraisal well. A well drilled several spacing locations away from a producing well to determine the boundaries or extent of a productive formation and to establish the existence of additional reserves.

      bbl. One stock tank barrel, or 42 U.S. gallons liquid volume, of crude oil or other liquid hydrocarbons.

      Bcf. Billion cubic feet of natural gas.

      Bcfe. Billion cubic feet equivalent, determined using the ratio of six Mcf of natural gas to one bbl of crude oil, condensate or natural gas liquids.

      Block. A block depicted on the Outer Continental Shelf Leasing and Official Protraction Diagrams issued by the U.S. Minerals Management Service or a similar depiction on official protraction or similar diagrams issued by a state bordering on the Gulf of Mexico.

      Btu or British Thermal Unit. The quantity of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

      Completion. The installation of permanent equipment for the production of oil or natural gas, or in the case of a dry hole, the reporting of abandonment to the appropriate agency.

      Condensate. Liquid hydrocarbons associated with the production of a primarily natural gas reserve.

      Deep shelf well. A well drilled on the outer continental shelf to subsurface depths greater than 15,000 feet.

      Deepwater. Depths greater than 1,300 feet (the approximate depth of deepwater designation for royalty purposes by the U.S. Minerals Management Service).

      Developed acreage. The number of acres that are allocated or assignable to productive wells or wells capable of production.

      Development well. A well drilled within the proved boundaries of an oil or natural gas reservoir with the intention of completing the stratigraphic horizon known to be productive.

      Dry hole. A well found to be incapable of producing hydrocarbons in sufficient quantities such that proceeds from the sale of such production exceed production expenses and taxes.

      Dry hole costs. Costs incurred in drilling a well, assuming a well is not successful, including plugging and abandonment costs.

      Exploitation. Ordinarily considered to be a form of development within a known reservoir.

      Exploratory well. A well drilled to find and produce oil or gas reserves not classified as proved, to find a new reservoir in a field previously found to be productive of oil or gas in another reservoir or to extend a known reservoir.

      Farm-in or farm-out. An agreement under which the owner of a working interest in an oil or gas lease assigns the working interest or a portion of the working interest to another party who desires to drill on the leased acreage. Generally, the assignee is required to drill one or more wells in order to earn its

interest in the acreage. The assignor usually retains a royalty or reversionary interest in the lease. The interest received by an assignee is a “farm-in” while the interest transferred by the assignor is a “farm-out.”

      Field. An area consisting of either a single reservoir or multiple reservoirs, all grouped on or related to the same individual geological structural feature and/or stratigraphic condition.

      Gross acres or gross wells. The total acres or wells, as the case may be, in which a working interest is owned.

      Lease operating expenses. The expenses of lifting oil or gas from a producing formation to the surface, and the transportation and marketing thereof, constituting part of the current operating expenses of a working interest, and also including labor, superintendence, supplies, repairs, short-lived assets, maintenance, allocated overhead costs, ad valorem taxes and other expenses incidental to production, but not including lease acquisition or drilling or completion expenses.

      Mbbls. Thousand barrels of crude oil or other liquid hydrocarbons.

      Mcf. Thousand cubic feet of natural gas.

      Mcfe. Thousand cubic feet equivalent, determined using the ratio of six Mcf of natural gas to one bbl of crude oil, condensate or natural gas liquids.

      MMBls. Million barrels of crude oil or other liquid hydrocarbons.

      MMBtu. Million British Thermal Units.

      MMcf. Million cubic feet of natural gas.

      MMcfe. Million cubic feet equivalent, determined using the ratio of six Mcf of natural gas to one bbl of crude oil, condensate or natural gas liquids.

      Net acres or net wells. The sum of the fractional working interests owned in gross acres or wells, as the case may be.

      Net revenue interest. An interest in all oil and natural gas produced and saved from, or attributable to, a particular property, net of all royalties, overriding royalties, net profits interests, carried interests, reversionary interests and any other burdens to which the person’s interest is subject.

      Payout. Generally refers to the recovery by the incurring party to an agreement of its costs of drilling, completing, equipping and operating a well before another party’s participation in the benefits of the well commences or is increased to a new level.

      PV10 or present value of estimated future net revenues. An estimate of the present value of the estimated future net revenues from proved oil and gas reserves at a date indicated after deducting estimated production and ad valorem taxes, future capital costs and operating expenses, but before deducting any estimates of federal income taxes. The estimated future net revenues are discounted at an annual rate of 10%, in accordance with the Securities and Exchange Commission’s practice, to determine their “present value.” The present value is shown to indicate the effect of time on the value of the revenue stream and should not be construed as being the fair market value of the properties. Estimates of future net revenues are made using oil and natural gas prices and operating costs at the date indicated and held constant for the life of the reserves.

      Productive well. A well that is found to be capable of producing hydrocarbons in sufficient quantities such that proceeds from the sale of such production exceed production expenses and taxes.

      Prospect. A specific geographic area which, based on supporting geological, geophysical or other data and also preliminary economic analysis using reasonably anticipated prices and costs, is deemed to have potential for the discovery of commercial hydrocarbons.

      Proved developed non-producing reserves. Proved developed reserves expected to be recovered from zones behind casing in existing wells.

      Proved developed producing reserves. Proved developed reserves that are expected to be recovered from completion intervals currently open in existing wells and capable of production to market.

      Proved developed reserves. Proved reserves that can be expected to be recovered from existing wells with existing equipment and operating methods. This definition of proved developed reserves has been abbreviated from the applicable definitions contained in Rule 4-10(a)(2-4) of Regulation S-X. The entire definition of this term can be viewed on the website at http://www.sec.gov/divisions/corpfin/forms/regsx.htm#gas.

      Proved reserves. The estimated quantities of crude oil, natural gas and natural gas liquids that geological and engineering data demonstrate with reasonable certainty to be recoverable in future years from known reservoirs under existing economic and operating conditions. This definition of proved reserves has been abbreviated from the applicable definitions contained in Rule 4-10(a)(2-4) of Regulation S-X. The entire definition of this term can be viewed on the website at http://www.sec.gov/divisions/corpfin/forms/regsx.htm#gas.

      Proved undeveloped reserves. Proved reserves that are expected to be recovered from new wells on undrilled acreage or from existing wells where a relatively major expenditure is required for recompletion. This definition of proved undeveloped reserves has been abbreviated from the applicable definitions contained in Rule 4-10(a)(2-4) of Regulation S-X. The entire definition of this term can be viewed on the website at http://www.sec.gov/divisions/corpfin/forms/regsx.htm#gas.

      Reservoir. A porous and permeable underground formation containing a natural accumulation of producible oil and/or gas that is confined by impermeable rock or water barriers and is individual and separate from other reservoirs.

      Shelf. Areas in the Gulf of Mexico with depths less than 1,300 feet. Our shelf area and operations also includes a small amount of properties and operations in the onshore and bay areas of the Gulf Coast.

      Subsea tieback. A method of completing a productive well by connecting its wellhead equipment located on the sea floor by means of control umbilical and flow lines to an existing production platform located in the vicinity.

      Subsea trees. Wellhead equipment installed on the ocean floor.

      Undeveloped acreage. Lease acreage on which wells have not been drilled or completed to a point that would permit the production of commercial quantities of oil or gas regardless of whether or not such acreage contains proved reserves.

      Working interest. The operating interest that gives the owner the right to drill, produce and conduct operating activities on the property and receive a share of production.

33,348,130 Shares

of

Common Stock

Prospectus

                    , 2006

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

      The following table sets forth estimates of all expenses payable by the registrant in connection with the sale of common stock being registered. The selling stockholders will not bear any portion of such expenses. All the amounts shown are estimates except for the registration fee.

      Our second amended and restated certificate of incorporation provides that a director will not be liable to the corporation or its stockholders for monetary damages for breach of fiduciary duty as a director, except for liability (1) for any breach of the director’s duty of loyalty to the corporation or its stockholders, (2) for acts or omissions not in good faith or which involved intentional misconduct or a knowing violation of the law, (3) under section 174 of the Delaware General Corporate Law (“DGCL”) for unlawful payment of dividends or improper redemption of stock or (4) for any transaction from which the director derived an improper personal benefit. In addition, if the DGCL is amended to authorize the further elimination or limitation of the liability of directors, then the liability of a director of the corporation, in addition to the limitation on personal liability provided for in our charter, will be limited to the fullest extent permitted by the amended DGCL. Our bylaws provide that the corporation will indemnify, and advance expenses to, any officer or director to the fullest extent authorized by the DGCL.

      Section 145 of the DGCL provides that a corporation may indemnify directors and officers as well as other employees and individuals against expenses, including attorneys’ fees, judgments, fines and amounts paid in settlement in connection with specified actions, suits and proceedings whether civil, criminal, administrative, or investigative, other than a derivative action by or in the right of the corporation, if they acted in good faith and in a manner they reasonably believed to be in or not opposed to the best interests of the corporation and, with respect to any criminal action or proceeding, had no reasonable cause to believe their conduct was unlawful. A similar standard is applicable in the case of derivative actions, except that indemnification extends only to expenses, including attorneys’ fees, incurred in connection with the defense or settlement of such action and the statute requires court approval before there can be any indemnification where the person seeking indemnification has been found liable to the corporation. The statute provides that it is not exclusive of other indemnification that may be granted by a corporation’s charter, bylaws, disinterested director vote, stockholder vote, agreement, or otherwise.

      Our charter also contains indemnification rights for our directors and our officers. Specifically, the charter provides that we shall indemnify our officers and directors to the fullest extent authorized by the DGCL. Further, we may maintain insurance on behalf of our officers and directors against expense, liability or loss asserted incurred by them in their capacities as officers and directors.

      We have obtained directors’ and officers’ insurance to cover our directors, officers and some of our employees for certain liabilities.

      We have entered into written indemnification agreements with our directors and executive officers. Under these agreement, if an officer or director makes a claim of indemnification to us, either a majority of the independent directors or independent legal counsel selected by the independent directors must review the relevant facts and make a determination whether the officer or director has met the standards of conduct under Delaware law that would permit (under Delaware law) and require (under the indemnification agreement) us to indemnify the officer or director.

      The registration rights agreement and purchase/placement agent agreement we entered into in connection with our earlier financings provide for the indemnification by the investors in those financings of our officers and directors for certain liabilities.

      In the last three years, we have sold and issued the following unregistered securities:

Item 17.     Undertakings.

      (a) The undersigned registrant hereby undertakes: