In, Has Peak Oil Come To The Non-Opec World? Maybe., Forbes advises investors that the traditional Western Big Oil firms have peaked, and to look elsewhere for profits from new production:
 

The world’s biggest oil companies put in a pretty pathetic performance in the second quarter of 2011. Not in terms of earnings — those were great, with Exxon posting $10.7 billion and Royal Dutch Shell doing $8 billion. Just what you’d expect with Brent crude at a lofty $120 a barrel.

Where the results were disappointing was in the barrels.  Of the 16 big U.S. and European oil companies studied by Deutsche Bank analyst Paul Sankey, 14 of them saw their production of petroleum decline in the quarter. Collectively, the drop amounted to 12% of total liquids volumes, or 1.2 million bpd. Their average output for the quarter totalled, 14.67 million bpd. Even excluding the effect of Libya’s issues, the decline was 8%.

...

What’s an investor to do? Buy oil companies of course, especially those that show any likelihood of boosting oil output. The only big one likely to do that this year, Occidental Petroleum, trades at 10 times expected 2011 earnings. Sankey also rates Canadian Natural Resources a buy, expecting eventual growth from its oil sands operations.

"Oil sands" is newspeak for tar sands. When oil prices are high enough, they can mine the bitumen and cook it into synthetic oil, but it's an environmental disaster. The Tar Sands Action sit-in is up to 595 arrests as celebrities and ordinary folk alike protest the proposed Keystone XL pipeline from Alberta to the Gulf.

Yesterday, Big Oil stalwart ExxonMobil announced a partnership with Russian oil giant Rosneft. In, Rosneft and ExxonMobil Plan $3.2B Program in Black, Kara Seas, Rigzone reports:
 

Rosneft and ExxonMobil have executed a Strategic Cooperation Agreement under which the companies plan to undertake joint exploration and development of hydrocarbon resources in Russia, the United States and other countries throughout the world, and commence technology and expertise sharing activities. ...

The agreement also provides Rosneft with an opportunity to gain equity interest in a number of ExxonMobil's exploration opportunities in North America, including deep-water Gulf of Mexico and tight oil fields in Texas (USA), as well as additional opportunities in other countries. The companies have also agreed to conduct a joint study of developing tight oil resources in Western Siberia.

I suspect the primary driver is that the conjoined firms expect to find a lot of oil in the Arctic. The ice is melting, Rosneft has local muscle (Putin) and ExxonMobil offers deepwater expertise.
 

The companies will create an Arctic Research and Design Center for Offshore Developments in St. Petersburg, which will be staffed by Rosneft and ExxonMobil employees. The center will use proprietary ExxonMobil and Rosneft technology and will develop new technology to support the joint Arctic projects, including drilling, production and ice-class drilling platforms, as well as other Rosneft projects.