French energy giant Total has decided to make a $1 billion investment in Iran to develop phase 11 of the South Pars gas project.

This is the first big energy investment in Iran since the 2015 sanctions relief deal. The South Pars offshore field was first developed in the 90s and Total was one of the biggest investors in the project before sanctions were imposed in 2006 over Iran's nuclear program.

Total CEO Patrick Pouyanne told Reuters "It is worth taking the risk at $1 billion because it opens a huge market. We are perfectly conscious of some risks. We have taken into account (sanctions) snap-backs, we have to take into account regulation changes,"

According to Pouyanne Total's share will be 50.1 percent along with state-owned China National Petroleum Corporation, with 30 percent, and Iran's Petropars with a 19.9 percent.

Other oil giants such as Royal Dutch Shell and BP showed limited interest to invest in Iran, due to uncertainty over contract terms and a sharp drop in global oil prices.