With fuel in acutely short supply in oil-rich Iraq, U.S. forces arrested 20 people and seized 28 gasoline tankers and nine propane trucks allegedly involved in a black market operation in Baghdad, the military reported Friday.

The U.S. sweep occurred Thursday as the Iraqi Oil Ministry (search) announced a rationing plan to overcome gasoline shortages throughout the country which has the world's second-largest oil reserves. Neighboring Saudi Arabia has the largest reserves.

In recent weeks, Iraqi drivers have endured fuel shortages akin to those that plagued the country after the March invasion by the U.S.-led coalition.

The official price of gasoline is about 5 U.S. cents a gallon. It can be as high as $1.85 a gallon on the black market.

In Baghdad, lines of cars at antiquated gas stations stretch more than a mile, and drivers line up overnight to beat the daylight rush. It can take 10 hours or more to reach the pumps from the end of the queue.

First Armored Division (search) soldiers detained 20 "black marketers" in the Thursday night raid, part of Operation Iron Justice (search), the military said. Commanders fear anti-U.S. rebels are benefiting from illegal gasoline sales to fund their insurgency.

"The operation is intended to combat corruption both to improve quality of life for the Iraqi populace and to deny former regime elements illegal sources of income," the U.S. military said in a statement.

The new Oil Ministry regulations require cars with odd license plate numbers and even plate numbers to fill up on alternate days. The regulations limit each car to about 8 gallons daily.

"The new policy is meant first and foremost to defuse the bottleneck at the gas stations and let as many people as possible get gasoline," Abdul-Sahib Salman Qutub, an Oil Ministry adviser.

"The measure is temporary and will be abolished when the situation is under control," Qutub said. However, lines at gas stations remained long on Friday.

War-damaged and antiquated refineries in Iraq and difficulties in bringing crude oil supplies back to sufficient levels are blamed for the shortages. As much as two-thirds of Iraq's gasoline supplies have been coming by truck from Turkey. There was a strike last week at the border, causing a severe slowdown in imports.

Also the country is awash in newly imported cars. About 250,000 cars are estimated to have entered Iraq from Turkey, Jordan and Syria over since the April ouster of Saddam Hussein.