UPDATE 2-Repsol in talks with Rosneft on Sakhalin stake

(Updates with stake size, adds background)

By Martin Roberts

MADRID, July 8 (Reuters) - Spanish oil company Repsol (REP.MC: Quote, Profile, Research) is in talks with Russian oil major Rosneft ROSNM.MM about taking a 24 percent stake in the Sakhalin-III oil and gas fields, a company spokesman said on Tuesday.

In a regulatory filing, the company said the stake would be worth $64 million, based on estimated investments in exploration in 2008 in the field.

The size of the stake would be linked to exploration work that was due to begin shortly in Sakhalin Island off Russia, which is majority controlled by Rosneft and about a quarter owned by China's Sinopec (600028.SS: Quote, Profile, Research).

"No deal has yet been reached, so a successful outcome to the talks may not arise," Repsol said.

Almost all global oil majors have set up large scale operations in Russia, the world's second-largest oil exporter.

While some enjoy Kremlin and state-owned companies' support other face problems, including BP's (BP.L: Quote, Profile, Research) oil venture TNK-BP.

Repsol bought a 10 percent stake in West Siberian Resources for $90 million in 2006 and in the same year signed a preliminary deal with state gas export monopoly Gazprom (GAZP.MM: Quote, Profile, Research).