EXXON Mobil Corp yesterday signed a deal with Russia's Rosneft to develop oil and gas resources in the Black Sea, a new boost for the country's lucrative energy sector, despite concerns about the challenges of investing there.

Exxon Mobil Chairman and CEO Rex Tillerson announced the deal with Rosneft Chairman Igor Sechin, who is also Russia's vice prime minister, at the World Economic Forum in Davos, Switzerland.

They did not disclose the potential value of the deal, but said it could lead to crude oil sales to Rosneft's Tuapsinsky refinery and other Black Sea markets.

The deal gives Exxon access to Russian resources and Russia access to Exxon's technology.

They will explore an 11,200-square-kilometer deep-water offshore area in Russia's sector of the Black Sea.