By Claudia Assis
SAN FRANCISCO (MarketWatch) -- Oil struggled to hold on to gains Monday, dipping in and out of the red following Friday's 4.1% losses, the worst single-day drop for crude since early February. Oil for July delivery, the most active contract, retreated 3 cents, or 0.04%, to $71.49 a barrel on the New York Mercantile Exchange. Oil for August delivery added 6 cents to $72.86 a barrel.
