France's Total SA said it would sign a deal to invest $1 billion in a giant Iranian gas field Monday, marking the first major investment in years by a Western company in the country's oil sector. Total will be the lead operator in a partnership with China National Petroleum Corp. and Iran's Petropars to develop South Pars -- a gas field under the Persian Gulf that is one of the world's largest. Iran's oil ministry said the contract would be signed Monday afternoon. The Paris-based oil giant has led the charge to return to the oil-rich country since Western sanctions over its nuclear program were lifted. Monday's deal will be the culmination of months of negotiations after Total signed a preliminary $4.8 billion agreement to develop the giant gas deposit alongside its partners late last year. Total Chief Executive Patrick Pouyanne has indicated the first $1 billion to be pledged on Monday would go toward funding the project's first phase. Total said the gas from the Pars field will supply the domestic market from 2021. The company had been in talks with Iran to create the country's first liquefied natural gas export system but they couldn't agree on a gas price, people familiar with the matter said.via