Iran says French energy giant Total is to sign a contract worth close to $5bn (£3.8bn) to develop an offshore gas field in the Gulf.
It is the biggest foreign deal since most economic sanctions against the country were lifted in 2016.
Oil ministry officials said the deal to develop the South Pars gas field would be signed on Monday in Tehran, with Total getting a 50.1% stake.
China's CNPC would hold a 30% stake and Iran's Petropars 19.9%.
Total was planning to sign the contract several months ago, but decided to wait and see if the Trump administration in the US would re-impose sanctions on Tehran.
The offshore field, which is shared between Iran and Qatar, was first developed in the 1990s.
Total was one of the biggest investors in Iran before international sanctions were imposed in 2006 over suspicions the country was trying to develop nuclear arms.
Last month Total's boss Patrick Pouyanne indicated the firm was ready to make an initial $1bn investment in Iran, the third largest producer in oil body Opec.