Updated from 12:57 p.m. EDTCrude oil prices rose for the fourth session in six on Thursday, closing above $40 a barrel for the first time in five weeks, as traders focused on the possibility of reduced production in Russia. The benchmark U.S. crude gained $1.12, or 3%, to $40.20, after closing lower Wednesday. Gasoline futures rose almost 5 cents, or 3.7%, to $1.32 a gallon. Russia's largest oil company, Yukos, is embroiled in a major tax dispute with the government, and there's speculation that the company could be driven into bankruptcy if it is forced to make a huge tax payment. Concerns about supplies from Russia come as Iraq once again struggles to restore exports to a normal level after problems with a pipeline over the weekend. The latest inventory data on oil and gasoline stockpiles was mixed. Prices have jumped more than $4 since last Tuesday, when they closed below $36 a barrel for the first time in three months. The recent rally took a pause Wednesday after Saudi Arabia -- the world's largest oil export and the dominant member of the Organization of Petroleum Exporting Countries -- signaled that the oil cartel had already decided to increase its production ceiling by half a million barrels a day in August. OPEC had previously said it would meet in July to consider the measure. The meeting isn't scheduled until July 21. The measure was part of a broader agreement reached at OPEC's June meeting, when it decided to increase official production by 2 million barrels a day in July. At one point, oil prices had fallen 15% from their record high of more than $42 a barrel reached the day before OPEC's June 3 meeting. During May, 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.