Cnooc Ltd. (0883.HK, CEO) is in talks with Norway's StatoilHydro ASA (STL.OS, STO) over a deal that would open the U.S. Gulf of Mexico to China's oil companies for the first time, a person familiar with the matter said.

The move is significant as Cnooc's aborted $18.5 billion bid for California-based Unocal Corp. (UCL) in 2005 is widely seen as having deterred state-owned Chinese oil giants from investing in U.S. oil and gas assets. Cnooc withdrew its offer for Unocal after it drew a storm of protests from some U.S. politicians.

But as tight credit has caused a lull in spending on offshore exploration, appetite for Chinese capital has grown, and opposition to Chinese investment may be less likely.

StatoilHydro, which has more than 400 leases in the U.S. Gulf of Mexico, is putting on the market only five prospects, said another person familiar with the situation. The prospects include the Tucker and Krakatoa deepwater fields, the person said.

The person, who didn't confirm or deny any Cnooc interest, said there's "huge interest" in the prospects and that the Norwegian oil company is negotiating with interested partners.

But StatoilHydro downplayed the significance of the sale.

"The fact is that we have opened dataroom for some leases that we acquired in the lease sale in 2007 and 2008, and where we have 100% ownership," said StatoilHydro spokesman Kai Nielsen. A dataroom is where vendors disclose information on the assets they're selling.

"This is a normal optimization of our portfolio, and a minor adjustment covering only a handful of licenses," Nielsen said. "We cannot confirm who is considering our offer."

The company didn't specifically deny being in talks with Cnooc.

The U.S. Gulf of Mexico remains one of the most plentiful areas of the world for oil discoveries, with billions of barrels of crude believed to be trapped below the seabed. This is attracting Chinese companies at a time when they are encountering difficulties in tying up deals elsewhere in the world, partly because oil-rich countries want greater control over their resources.

Earlier this year, a senior executive of Chevron Corp. (CVX) confirmed the U.S. major held talks over selling a minority interest in the Big Foot oil field in the Gulf of Mexico to China National Petroleum Corp. The talks were suspended in March, with a CNPC official saying at the time that CNPC found the stake offered too small.

Devon Energy Corp. (DVN) Chief Executive Larry Nichols said last month that Devon's ongoing sale of up to 50% of its stakes in deepwater blocks in the Gulf of Mexico has attracted interest from national oil companies, including those seeking to enter the sector for the first time, a description that would fit Chinese state firms.

Cnooc could be the first Chinese firm to actually clinch a deal in the coveted region.

"Cnooc expects to sign a deal with StatoilHydro soon to buy stakes in some deepwater exploration blocks in the U.S. Gulf of Mexico," said one of the people familiar with the situation, declining to specify the assets involved.

Cnooc board secretary Xiao Zongwei declined to comment.

China's oil companies no longer need foreign capital and are increasingly confident they have the technology to develop domestic oil and gas fields by themselves rather than bring in a partner from abroad.

As a result, deals in China are frequently conditional on foreign companies agreeing to let the Chinese take part in overseas projects. Chevron's offer of a stake in Big Foot signaled that the U.S. oil major felt it had to offer something in return for its selection by CNPC's listed unit PetroChina Co. (PTR, 601857.SH) as its partner in the large Chuandongbei natural gas project in southwestern China. Such dealmaking is likely to be a key factor in a potential Chinese presence in U.S. oil fields.

StatoilHydro's interest in negotiating a deal with Cnooc likely reflects its difficulty in securing new projects in China. In April, the company said it planned to shut down the depleted Lufeng 22-1 field in the South China Sea, which was its only producing asset in China. StatoilHydro was among the companies that expressed interest in the Chuandongbei project, but lost out to Chevron.

In addition, StatoilHydro could lower exploration risk and costs by bringing Cnooc into some of its acreage in the Gulf of Mexico, where it has an extensive presence.

According to StatoilHydro's Web site, the company has 448 active leases in the U.S. Gulf of Mexico, including some of the biggest discoveries such as Jack, Tahiti and St Malo.

Analysts say China's oil companies should look to become junior partners of large Western companies if they want to build a position in the U.S., as this would be more acceptable to U.S. politicians.

Cnooc's decision to take a new look at the U.S. offshore oil and gas sector may reflect the challenges it has faced in expanding its overseas operations, especially in Africa.

Last month, Angola's state-owned Sonangol said it wanted to block the $1.3 billion sale of a 20% stake held by Marathon Oil Corp. (MRO) in an offshore oil block to Cnooc and China PetroChemical Corp. (SNP, 600028.SH), or Sinopec.

Cnooc also appeared to have lost out on the $4 billion sale of a stake in a giant oil discovery in West Africa when Kosmos Energy picked ExxonMobil Corp. (XOM) as the preferred bidder earlier this month.

However, Cnooc is in advanced talks with Ghana National Petroleum Corp. about making a rival bid for Kosmos's stake in the Jubilee field, estimated to hold 1.8 billion barrels of oil, people familiar with the matter say.

-By David Winning and Russell Gold, Dow Jones Newswires; +61-2-82724688; david.winning@dowjones.com

(Jing Yang, Elizabeth Adams and Guy Chazan contributed to this article.)