In a separate attack northeast of Baghdad, four people were killed in a separate suicide bombing targeting a funeral procession for two members of an anti-al Qaeda, officials said.
Local authorities said victims were still being pulled from the rubble of two destroyed buildings and that the death toll was expected to rise.
The bomber, who was driving a pickup truck, detonated his explosives when Iraqi police and members of a volunteer security force prevented him from entering the gate of the compound belonging to the state-run North Oil Company in Beiji, about 155 miles north of Baghdad, a police officer said. He said some of the residential buildings were damaged in the blast.
Most of the 22 killed were civilians, and at least three were children, the police officer said. The dead also included guards of the oil company and members of the volunteer force.
An official at the main hospital in Beiji gave the same casualty figures and said 65 were wounded.
Both officials spoke on condition of anonymity because they were not authorized to release information to the media.
The U.S. military said in a statement that 20 people were killed and 80 wounded. The reason for the discrepancy in casualty figures was not immediately clear.
The wounded, bloodied and bandaged were crowded into the rooms and hallways of the Beiji General hospital. Three bodies - one of a child - were laid out on the floor, covered with white sheets.
Authorities imposed a curfew on the city - home to the country's largest refinery - until further notice.
Volunteer forces known as Awakening Councils - groups of Sunni Arab fighters who have turned against al Qaeda and are now funded by the U.S. - have been credited with helping reduce violence in Iraq in recent months. Although bombings and other attacks continue throughout the country, their number has fallen. The U.S. military has said there has been a 60 percent decrease in violence since June.
Iraq's oil industry and those who work in it have come under repeated attack since the U.S.-led 2003 invasion, usually through bombings of key pipelines. Revenue from the oil industry is seen as key to funding Iraq's reconstruction and sparking economic recovery.
In Baqouba, 35 miles northeast of Baghdad, a suicide bomber detonated himself amid mourners at a funeral. At least four people were killed and 21 injured, a police officer said on condition of anonymity as he was not authorized to release the information.
The funeral was being held for two members of a U.S.-backed anti-al Qaeda in Iraq group.
Meanwhile, the U.S. military said troops killed 13 suspected insurgents and detained another 27 on Monday and Tuesday in operations targeting al Qaeda in Iraq in the central and northern parts of the country.
Iraq has been enjoying one of its most peaceful holiday seasons in years, but fear of violence persists, and the country's first cardinal made a Christmas appeal Monday for those who have fled to return and help rebuild their shattered country.
Cardinal Emmanuel III Delly, leader of the ancient Chaldean Church, told The Associated Press at his guarded compound in west Baghdad that his message was one of love and for "charity towards everyone.
"And for the emigrants to return home, to work for the good of their country and their homeland despite the situation which their country is in. That is my hope."
President Bush made Christmas Eve calls to 10 U.S. troops serving in Iraq, Afghanistan and other spots around the world, thanking them for their sacrifice and wishing them a happy holiday even though they'll be far away from their families and friends.
The president made his calls Monday from the Camp David presidential retreat in the Maryland mountains, where he is spending Christmas. He spoke with members of the Army, Navy, Marines, Air Force and U.S. Coast Guard, including seven serving in Iraq.
White House press secretary Dana Perino said Mr. Bush knows it is difficult for the children of U.S. servicemen and women to understand why their fathers and mothers cannot be home for the holidays. Mr. Bush said that when the children are older, he hopes they'll understand and appreciate their parents' sacrifice, Perino said.
So far the holiday season has been peaceful. Last year, more than 2,300 people died in war-related violence, compared to about 540 so far this month, according to an Associated Press count.
Violence has fallen across the country by 60 percent since June, according to U.S. military figures. But security is still poor and few Iraqis dare stray too far from home. The threat of kidnapping, car bombs and suicide bombers is never far, and the dead bodies of tortured kidnap victims turn up almost daily along river banks or dumped on the streets.
Sectarian violence has declined largely because of a surge by thousands of U.S. troops, the help of Sunni Arab irregulars who have turned against al Qaeda in Iraq and are now funded by the United States, and a cease-fire by radical Shiite cleric Muqtada al-Sadr and his Mahdi Army.