BAGHDAD — Iraq’s government sold development rights to two of its largest untapped oil fields at a public auction held under extraordinary security on Friday, three days after a series of coordinated bombings killed more than 100 people here in the capital.

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A partnership of Royal Dutch Shell and Petronas, a state-owned Malaysian company, won the larger field, Majnoon, in southern Iraq, which contains an estimated 12.6 billion barrels of recoverable oil.

The second field, Halfiya, also in the south, was won by a consortium led by China National Petroleum Company that included Petronas and Total of France. It is believed to hold some 4.1 billion barrels.

The auction, the second since the 2003 invasion, attracted representatives of dozens of the world’s largest oil companies, including ExxonMobil, British Petroleum and Russia’s Lukoil. “I was nervous when I was sitting there,” said Mounir Bouaziz, a vice president at Shell, after he submitted the winning bid for the Majnoon field. “We are pleased and relieved to have won this. It has taken a lot of work to get this, including months and months of study and discussions.”

The event, shown on Iraq’s state-owned television channel, was held in the Oil Ministry under security tight by even Baghdad’s heavily policed standards. Helicopters circled overhead; thousands of police officers and soldiers patrolled roadways; streets within a mile of the ministry were closed to all vehicles but the convoys of armored S.U.V.’s ferrying oil executives; and everyone who made it inside was subjected to body searches.

Increasing oil revenue is crucial for the Iraqi government, to finance security and reconstruction efforts. Prime Minister Nuri Kamal al-Maliki gave optimistic introductory remarks, thanking oil executives for attending and saying their presence signaled “confidence” in Iraq.

“There is no security deterioration in Iraq, even if a security breach occurred,” Mr. Maliki said. “Iraq is on its way to removing all its obstacles.”

There is no question that the companies were facing disquieting issues. Political squabbling has delayed critical national elections from January until March, even as American troops are scheduled to continue withdrawing from Iraq. Because Parliament has been unable to approve a national oil law, it is unclear whether agreements reached with oil companies before the March 7 election will be recognized by a new government if Mr. Maliki fails to regain his post.

Shell’s main competition for the Majnoon field came from Total, which has a long history there. Total signed an agreement with Saddam Hussein in the 1990s to develop the field, a pact that Mr. Hussein annulled in 2002. Two years ago, Total and Chevron signed an agreement to explore it.

But Friday, while Total and its partner, the Chinese National Petroleum Company, offered to accept a $1.75 fee for each barrel produced at Majnoon, the partnership of Shell and Petronas submitted a bid at $1.39 per barrel. While the Shell group gave a guarantee that it would produce 1.8 million barrels a day at Majnoon, the Total group pledged only about 1.4 million barrels.

As for the Halfiya field, the Chinese National Petroleum Company has a 50 percent stake in the winning consortium, while Total and Petronas have shares of 25 percent each.

If the group eventually signs a development contract with the Iraqi government, it would be the third Iraqi oil field development deal won by the Chinese company during the past year. In November 2008, it signed a contract to develop the Ahdab field southwest of Baghdad. Last month, it agreed to develop the 17.8-billion-barrel Rumalia field with British Petroleum.

Three oil fields had no winning bidders on Friday; all are in areas where attacks remain relatively frequent, including the East Baghdad field, which lies beneath the Sadr City district. Several schoolchildren were killed in a bombing there this week.

The auction is to continue Saturday, with five more fields offered.

Duraid Adnan and Mohammed Hussein contributed reporting from Baghdad, and Jad Mouawad from New York.

A version of this article appeared in print on December 12, 2009, on page A8 of the New York edition.