The state-controlled Russian energy company Gazprom agreed Wednesday to purchase a majority stake in privately owned Sibneft for $13.01 billion, the largest corporate deal in Russia's history and one that will tighten the state's grip on the country's booming energy sector.

Gazprom, formed from assets of the Soviet natural gas ministry, will acquire 72.66 percent of Sibneft's shares. The sale will be almost completely financed with a loan of $12 billion from a consortium of Western banks.

Gazprom will buy the shares from a holding company controlled by Roman Abramovich, a Russian billionaire who has close relations with the Kremlin.

Sibneft, Russia's fifth-largest oil producer, pumps about 900,000 barrels a day. The company emerged from the sale of state assets to private investors after the collapse of the Soviet Union, a policy that was unpopular here and is being reversed by President Vladimir Putin.

"The state is continuing its drive to control the oil sector and its strategic development," said Caius R. Rapanu, senior energy analyst at Nikoil Capital Market Research in Moscow.

Gazprom earlier bought 3 percent of Sibneft through its banking arm, and because it will now own more than 75 percent of the company, Russian law will allow it to exercise complete control over its decisions.

"The businesses of Gazprom and Sibneft have a defined synergy. This will make Gazprom more effective both in Russia and on the world oil and gas markets," Alexei Miller, chief executive of Gazprom, the world's largest producer of natural gas, said in a press release. "We are consistent in achieving our strategy goal of diversifying our business and turning Gazprom into a world-class, global energy company. Oil is now a core aspect of Gazprom's business."

Miller has said in the past that he intends to make Gazprom one of the world's great energy companies, rivaling Western giants such as Exxon Mobil Corp., BP PLC, and Royal Dutch Shell PLC. Thirty percent of Russia's oil production is now directly controlled by the state, which also exercises great influence on those assets it does not formally control.

Industry analysts noted that the purchase price works out to about $3.30 per barrel of reserves, a cut-rate price compared with other large oil deals. But the acquisition included a political calculation on Abramovich's part, some analysts said.

"If this had gone to an open international tender, it could have gone for twice as much," said William F. Browder, chief executive of Hermitage Capital Management in Moscow. "But given the provenance of these assets, he was probably happy to take $13 billion off the table. Look at the other major oil guy who tried to sell a strategic asset. Thirteen billion dollars is better than zero."

Browder was referring to Mikhail Khodorkovsky, the former head of the oil company Yukos who is serving an eight-year prison sentence for tax evasion and fraud in what his supporters call a politically motivated prosecution for his perceived political activities against the Kremlin.

Khodorkovsky had explored a merger with a Western oil giant before his arrest.

Last year, the Russian government broke up Yukos to settle what it called back taxes. In December, the state-owned oil company Rosneft acquired Yukos's prize asset, the Yuganskneftegaz oil fields, which pump about 1 million barrels of oil a day. The sale was criticized by Yukos's management as state-sanctioned theft.

"The reason Abramovich wanted to sell is that he didn't want to be subject to the arbitrary whim of the Russian government," Browder said.

Abramovich, the governor of Chukotka in Russia's remote Far East, has remained on good terms with the Kremlin, unlike many of his counterparts who made fortunes in the 1990s.

He is best known in Europe for his control of the Chelsea soccer club in London. He has put hundreds of millions of dollars into the team to obtain some of the world's best players. That investment paid off this year when Chelsea won the 2004-05 Premiership league title.

Roman Abramovich, right, whose holding company will sell controlling interest in Sibneft to state-owned Gazprom, met with Russian President Vladimir Putin in May. The $13.01 billion deal is the largest ever in Russia.