WRAPUP 1-Refining's silver lining loses luster at Exxon and Chevron

HOUSTON, April 29 (Reuters) - Exxon Mobil Corp and Chevron Corp posted sharp drops in quarterly results on Friday as an oversupplied fuel market shrank profits from their refining units, which until now had provided healthy margins that helped insulate them from a 60 percent slide in oil prices since mid-2014.