Updated from 12:14 p.m. EDT
Oil prices retreated Monday, closing below $38 a barrel again, following the end of a brief strike in the major oil-producing nation of Nigeria on Friday.
The benchmark U.S. crude fell 81 cents, or 2.1%, to $37.84, while gasoline prices fell 4.1 cents, or 3.4%, to $1.147 a gallon.
The general strike in Nigeria, which is also a member of the Organization of Petroleum Exporting Countries, had only a modest impact on the market late last week. The strike was over high gasoline prices.
Prices are now some 12% below their record high of two weeks ago, prior to OPEC's meeting, when its members agreed to increase production up to 2.5 million barrels a day this summer.
Strong global demand and worries about terrorist strikes on facilities in the oil-rich Persian Gulf have boosted prices to all-time highs through most of May.
Traders also bid up prices ahead of the peak summer driving season in Europe and America. Gasoline prices are now above $2 a gallon in many U.S. states.