From bloomberg today:

Exxon Lowers Bar, Buys Assets Once Seen Unattractive:

March 9 (Bloomberg) -- Exxon Mobil Corp., BP Plc and Total SA are investing in assets that previously weren’t worth their time or money after oil-rich nations reduced access to reserves and exploration drilling faltered.

Efforts to find new sources of crude and natural gas are failing more often, with San Ramon, California-based Chevron Corp.’s exploration failure rate jumping to 35 percent last year from 10 percent in 2008. Countries such as Venezuela are making it more expensive for companies to develop their resources, if they’re allowed in at all. And previously developed fields are drying up, reducing oil companies’ future supplies, or reserves.

“Their No. 1 problem is reserves replacement,” said Nansen Saleri, chief executive officer at Quantum Reservoir Impact in Houston and former reservoir-management chief at Saudi Arabia’s state oil company. “That’s the elephant in the room, so that’s what they have to address.”

To compensate, major producers are investing in projects they once eschewed, including geologically complex oil and gas fields, called “unconventional” by the industry to distinguish them from the easy-to-get oil and gas of earlier years.

Irving, Texas-based Exxon agreed to buy gas producer XTO Energy Inc. for $29 billion in December, 14 months after abandoning its own drilling program in Texas’s Barnett Shale unconventional gas formation, where XTO gets more than 20 percent of its output. BP, Total and Statoil ASA bought into U.S. shale-gas joint ventures, and Marathon Oil Corp. and ConocoPhillips are investing in unconventional gas in Europe.

http://www.bloomberg.com/apps/news?pid=20601109&sid=acubV2MKZMA0&pos=10