Exxon Mobil Corp and Russian partner Rosneft have signed an agreement that will give the US company exploration access to an additional 606,000 sq kilometres in the Russian Arctic.

A separate agreement will give Rosneft the opportunity to acquire a 25 percent interest in the Point Thompson unit on Alaska's North Slope.

The companies also said on Wednesday they will study a potential liquid natural gas project in the Russian Far East.

The agreements were announced Wednesday on the website of Irving, Texas-based Exxon Mobil. Rosneft President Igor Sechin and Exxon Mobil Exploration Co President Stephen Greenlee signed the agreements in Moscow in the presence of Russian President Vladimir Putin.

The agreements will give Exxon exploration access to seven new blocks in the Chukchi Sea, Laptev Sea and Kara Sea.

"The agreements signed today bring the already unprecedented scale of the Rosneft and ExxonMobil partnership up to a completely new level," Sechin said in the announcement.

"The acreage in the Russian Arctic subject to geological exploration and subsequent development increased nearly sixfold."

Top partner

Participation in Point Thomson, Sechin said, would increase Rosneft's access to the latest gas and condensate field development technologies used in harsh conditions.

ExxonMobil struck its deal during an international scramble that followed the unexpected collapse of a similar agreement Rosneft had initially been expected to sign with the US firm's British rival BP.

Rosneft has since signed identically-structured exploration deals with ENI of Italy and Norway's Statoil.

The international companies receive minority stakes in the Russian-run projects and are responsible for covering the initial exploration and development costs.

But Wednesday's agreement confirms ExxonMobil's status as Russia's most important energy partner by far.

The US giant said that Rosneft in return had the option of acquiring a 25-percent stake in its Point Thomson project - fields that ExxonMobil owned for decades but could only start developing recently following necessary

approval from the government.

The Point Thomson unit is 100 kilometres east of Prudhoe Bay and 35km east of the trans-Alaska oil pipeline. Alaska officials have said Point Thompson's importance transcends field development because it is the first project that will connect the trans-Alaska pipeline to eastern North Slope development.

Point Thomson is considered primarily a natural gas field and estimated to contain about 300 million barrels of gas condensate liquids, and traditional crude oil. Its development is considered critical to development of an Alaska natural gas pipeline.

The state of Alaska moved to terminate leases at Point Thomson after concluding that Exxon and other companies were not taking adequate steps to develop them.

However, after litigation, the state last year reached a settlement that called for development of the field.

The US Army Corps of Engineers in October issued a permit allowing Exxon Mobil and PTE Pipeline LLC to fill 108 hectares of North Slope waters and tundra wetlands to construct a drilling project.

The Exxon Mobil agreement with Rosneft on LNG development includes possible construction of a facility in the Russian Far East.

The companies said they would form a working group that will study the viability of an LNG project.