ANALYSIS-U.S.-Iran thaw may bring big oil cash back

By Simon Webb and Hashem Kalantari

DUBAI/TEHRAN, Feb 10 (Reuters) - International oil companies are reassessing, cautiously, the risk of investment in Iran after U.S. President Barack Obama offered direct talks with Tehran.

Obama has yet to define his policy, but signalled his expectation on Monday that a new relationship could begin within months.

Western firms may move more slowly than that and need a clear improvement in ties before acting, especially ahead of June presidential elections in Iran, the world's fourth-largest oil exporter.

"The big oil companies are looking at Iran again," said one oil company executive. "They have to. The potential gains are too big to ignore."

The administration of George W. Bush pressured any country or company that courted Iran for energy deals to stay out, as the United States aimed to isolate it over its disputed nuclear programme.

Washington's sanctions have barred U.S. firms investing in Iran's oil and gas sector since 1995 and include provisions to deter companies from other countries investing.

Royal Dutch Shell (RDSa.L: Quote, Profile, Research) and Total (TOTF.PA: Quote, Profile, Research) delayed decisions on multi-billion dollar investments in Iranian liquefied natural gas (LNG) plans last year due to political tension.

The political landscape could change again with an Iranian presidential election in June that will see hardline President Mahmoud Ahmadinejad pitted against Mohammad Khatami, who pursued detente with the West when in office from 1997-2005.