In China's latest big overseas oil deal, government conglomerate CITIC Group plans to buy Nations Energy Co.'s oil assets in Kazakhstan for $1.91 billion, the companies said Thursday.

The purchase, which requires approval by Calgary, Canada-based Nations Energy shareholders and the governments of Canada and Kazakhstan, would be China's third-largest acquisition of overseas oil assets.

Privately held Nations Energy's controlling shareholder, Ecolo Investments Ltd., has agreed to back CITIC's offer deal unless the company receives a superior one before the purchase is finalized, the companies said in a statement. Ecolo owns 76 percent of Nations Energy.

The deal is due to be completed in December, it said.

"We believe this is a fair price for Nations Energy shareholders and optionholders and the board of directors has unanimously agreed to recommend this transaction," David G. Wilson, a director for Nations Energy, said in the statement.

The purchase is only of Canada-based Nations Energy's biggest asset, the Karazhanbas field in Kazakhstan, which has proven oil reserves exceeding 340 million barrels, and current production of over 50,000 barrels of oil a day.

The company said it plans to divest itself from smaller assets it has in Azerbaijian, Indonesia and California.

CITIC, which has significant infrastructural investments in Central Asia, is planning to build a medium-sized refinery at Karazhanbas, said Zhang Jijing, a CITIC Group director.

"This is an excellent platform for CITIC's further diversified investment and business cooperation in Kazakhstan," Zhang said in the statement.

China has moved aggressively to buy up energy assets overseas to help fuel its booming economy and improve its energy security.

Last year, state-owned China National Petroleum eclipsed Russian rivals to acquire an oil field in Kazakhstan for $4.2 billion and built a pipeline to carry Kazakh crude to China.

In April, CNOOC, the country's offshore oil producer, acquired a $2.3 billion stake in a Nigerian offshore oil field.

China Petrochemical Corp., or Sinopec Group, in late June agreed to buy Anglo-Russian oil producer TNK-BP Holdings oil production unit Udmurtneft for $3.5 billion. But the deal called for it to sell 51 percent to Russian state oil company OAO Rosneft.

The Karazhanbas field was discovered in the 1970s and was in decline when Nations Energy acquired it in 1997 and drilled new wells, upgraded existing wells and added new production facilities, according to the company's Web site.

According to the Nations Energy's Web site, the company's chairman is Indonesian tycoon Hashim Djojohadikusumo, a son of Sumitro Djojohadikusumo, who was an economic advisor to former dictator Suharto, who stepped down in 1998 amid riots and protests after 32 years in power.

Nations Energy had been seeking a buyer for more than a year and reportedly unsuccessfully tried to sell itself to China National Petroleum Corp. and CNOOC Corp.

CITIC Group is one of China's biggest conglomerates. It was set up in Hong Kong in 1979 by former Vice President Rong Yiren as the government's main overseas investment arm.

CITIC Resources, a unit of CITIC Group with shares traded in Hong Kong, recently bought a 51 percent stake in an Indonesian field for $97.4 million.