Updated from 3:23 a.m. EDT
Oil prices ended lower Wednesday, following the release of a key government report on energy inventories.
The benchmark U.S. crude closed 68 cents, or 2%, lower at $37.57 in regular floor trading on the New York Mercantile Exchange. Gasoline prices were flat at $119.5 a gallon.
The Department of Energy's report showed oil stockpiles up by 2.5 million barrels in the most recent week, which exceeded market expectations.
Traders also focused on several other supply issues at home and abroad.
Norwegian oil workers are expected to expand their strike, further curbing production in the world's third-largest oil exporting nation.
Repair work continues on pipelines feeding Iraq's southern export complex, as periodic sabotage attacks against the industry infrastructure hurt output there.
And several U.S. refineries experienced unscheduled maintenance shutdowns recently.
Oil prices gained Tuesday, following a 3% slump Monday triggered by the resumption of more than half of Iraq's exports that day.
Repairs were completed on one of two major pipelines feeding the country's main southern export terminals that were damaged in attacks last week. Iraq's exports returned to about 1 million barrels a day.Iraqi exports have ranged between 1.6 million and 1.8 million barrels a day recently. Fellow members of the Organization of Petroleum Exporting Countries have pledged to compensate for any short-term supply disruption, but it remains unclear how long it will take to fully restore exports.
Oil prices had fallen about 12% from their record high of more than $42, touched right before OPEC's meeting two weeks ago. Prices briefly fell through $37 last week.
Members of the cartel agreed to raise the group's production quota by 2 million barrels a day in July and another half-million barrels a day in August, should that prove necessary. The current ceiling is 23.5 million barrels a day. Market analysts say the move is largely symbolic because the cartel's members are already producing some 2 million barrels a day above their official quotas.
Traders bid up prices on short-term supply concerns triggered by strong global demand and terrorist attacks on oil industry personnel and facilities in the Persian Gulf region ahead of the peak summer driving season in the U.S. and Europe.