The Iraqi government originally tried last year to award oil fields to Western companies through a no-bid process. That prompted objections from a group of United States senators, who wanted greater transparency, and the plan was replaced with the auction, which had the effect of letting Chinese companies play a much larger role.

China’s leaders were surprised by the steep rise in commodity prices early last year, which exposed the vulnerability of their country’s huge manufacturing sector to high raw material prices. When oil prices plunged in the autumn, China began buying, importing and storing oil in huge quantities, helping to drive a partial rebound in world oil prices in spring. And China stepped up its hunt to acquire foreign oil.

Chinese officials, economists and advisers have been almost unanimous in recent weeks in saying that their country needed to invest more in natural resources, while also voicing concerns about the long-term creditworthiness of the United States and the buying power of the dollar.

China has $2 trillion in foreign exchange reserves, mostly invested in dollar-denominated bonds, and has been looking for ways to diversify gradually into other assets like commodities, said a Chinese government adviser who spoke on the condition of anonymity because of the secrecy of Chinese reserve policies.

China’s central bank, the People’s Bank of China, called Friday for the development of an international currency other than the dollar that would be a safe repository of value, in the latest sign of China’s search for other ways to invest its international reserves.

Philip Andrews-Speed, a specialist in China’s oil industry at the University of Dundee in Scotland, said Iraq was clearly attractive for China and its oil industry.

“All, or nearly all, oil companies who have the courage want to be in Iraq because of the large size of the proven resource base and the potential for new discoveries,” he wrote in an e-mail message. “So, in this respect, the Chinese are part of the herd.”