Two of the world's largest energy companies have agreed to jointly search for oil in the Russian Arctic.

U.S.-based Exxon Mobil — the world's largest oil company — and Rosneft — the top Russian crude oil producer — signed a $3.2 billion agreement Tuesday. The companies said they plan to explore for oil in the depths of the Arctic in the Kara Sea, as well in the Black Sea.

The deal will also allow Rosneft to join development projects in the southwestern U.S. state of Texas, and in the Gulf of Mexico off the southern U.S. shoreline.

The agreement was personally sanctioned by Russian Prime Minister Vladimir Putin, who met with Exxon chief executive Rex Tillerson in the Russian Black Sea resort city of Sochi. Mr. Putin said the two companies may eventually spend as much as $500 billion on joint projects. Tillerson said the initial agreement would create “substantial value” for both companies.

Energy experts say the Kara and Black sea sites are among the world's most promising for finding more oil, as well as natural gas, yet they are among the least explored offshore locations.