The agreement seemed to supersede a similar but now-defunct partnership that Russia’s state oil company, Rosneft, reached with BP earlier this year. The deal announced Tuesday replaces BP, the British oil giant, with its American counterpart and introduces some differences in the geopolitical bargain.

Where BP had swapped stock, Exxon agrees to hand over to Rosneft unspecified assets elsewhere in the world, including some that the Texas-based company owns in the deepwater zones of the Gulf of Mexico and onshore in Texas.

It was not immediately clear whether Rosneft would gain operational control of any Texas or Gulf of Mexico sites or merely obtain a portion of the equity in the projects.

Either way, Exxon’s concessions in the agreement further a long-held goal of the Russian petroleum industry to diversify internationally, using access to reserves at home as leverage to win the capital and technological expertise to do so.

In the announcement of the arrangement, coming after a surprise signing in the Russian resort town of Sochi, Prime Minister Vladimir V. Putin described a sweeping global alliance — and a potentially vast investment by Exxon in the Russian Arctic.

Mr. Putin said the total investments envisioned under the agreement could reach $500 billion, including a direct investment of $200 billion to $300 billion. It was unclear what the timeline would be or whether this included the value of asset swaps.

A fact sheet released by the companies suggested an initial commitment to invest $3.2 billion in exploration in the Kara Sea, the body of water between the northern coast of European Russia and the Novaya Zemlya island chain.

Once seen as a useless, ice-clogged backwater, the Kara Sea has become the focus of attention by oil companies in part because the sea ice appears to be receding, possibly because of global warming, easing exploration and drilling. Russian scientists say the extent of the ice floes vary greatly from summer to summer, and conditions remain always formidable during the months-long polar night.

Gazprom, the Russian natural gas giant, this summer moved a rig into a shallow portion of the sea. In the waters off Alaska, drilling has remained largely off limits because of environmental restrictions and lawsuits by conservation organizations.

For Exxon, which is America’s largest company, the deal means wading deeper into Russia’s risk-fraught business environment. As a result of the deal, the safety of more of the company’s investments and future earnings will depend on policies set in the Kremlin.

Russia has reneged on deals before. Until this year, Exxon’s principal investment in Russia was a production sharing agreement on Sakhalin Island. This form of contract waives local taxes, providing the host government a share of the oil instead, and is seen as less risky.

After the failure of the BP deal, however, the onus is now on Russia to demonstrate it can uphold an agreement, said Cliff Kupchan, a senior analyst at Eurasia Group, in a telephone interview.

“They got away with BP, because the deal was seen as BP having two Russian wives,” he said. Exxon, in contrast, has no exclusivity clause with a competitor in Russia that could come up in court.

Under the joint venture with Rosneft, Exxon would explore three blocks. The BP deal had involved two exploration blocks. The agreement also included an offshore exploration deal Exxon struck with Rosneft in the Black Sea earlier this year.

“The scale of the investment is very large,” Mr. Putin said at the signing ceremony. “Exxon Mobil is definitely one of the leading companies, including for operations in the challenging Arctic latitudes.”

The agreement emerged as a modified version of the deal between BP and Rosneft, which was voided by a Stockholm arbitration panel after BP’s other business partners in Russia sued to block it.

In that arrangement, BP and Rosneft agreed to a swap of shares that would have resulted in Rosneft owning about 5 percent of BP’s shares. The Exxon agreement, in contrast, outlined a wide-ranging exchange of assets.

The failed BP agreement was also endorsed by Mr. Putin and his chief aide for oil and gas deals, Igor Sechin, a deputy prime minister. Analysts of Kremlin politics say an emerging schism in the leadership and infighting between Russian business clans resulted in the deal’s demise, despite this apparent high-level backing.

With Exxon now entering a similar agreement with similar official endorsements, the mercurial and risky nature of Russian petroleum politics is now a focus for the Irving, Tex.-based company, a spin-off of the original Standard Oil, particularly if the deal’s scale matches what Mr. Putin suggested it might.

Article source: http://www.nytimes.com/2011/08/31/business/global/exxon-and-rosneft-partner-in-russian-oil-deal.html?partner=rss&emc=rss