Updated from 1:05 p.m. EDTOil prices slipped, closing below the $41-a-barrel level Thursday, after registering a five-week high Wednesday. The benchmark U.S. crude lost 22 cents, or 0.5%, to $40.93, having jumped 4% yesterday. Gasoline futures, however, continued to rise, adding half a cent to $1.32 a gallon. The small decline came even though the Organization of Petroleum Exporting Countries said it had decided on an increase in its production ceiling of half a million barrels a day by August, and also cancelled a July 21 meeting on the issue. The measure was part of a broader agreement reached at OPEC's June meeting, when it decided to increase official production by two million barrels a day in July. At one point recently, oil prices had fallen 15% from their record high of more than $42 a barrel, reached the day before OPEC's June 3 meeting. Since then, prices have bounced back on worries about production levels in such major oil-producing countries as Iraq, Norway, Nigeria and Russia, as well as terror attacks on the U.S. ahead of the presidential election. During May, traders relentlessly bid up prices on short-term supply concerns triggered by strong global demand and terror 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.