Iran will sign a deal on Tuesday with French oil giant Total SA to help develop phase 11 of the giant offshore South Pars gas field which is shared by Iran and Qatar, according to an oil-ministry official in Tehran cited on Monday by the Wall Street Journal.

The so-called “heads of agreement” to develop phase 11 of the giant South Pars gas field will also include the China National Petroleum Corporation and the Islamic Republic’s state-owned Petropars, and will represent an investment of $6 billion. The agreement is a key step toward the return of Western companies to Iran’s giant fields, after a nuclear agreement with world powers ended international sanctions on its oil industry in January. The South Pars field contains 14,000 billion cubic meters of gas, eight percent of the world’s known reserves.