Iran’s South Pars development phases 17-21 will add more than 150 million cu m per day of new gas production from the giant Iranian offshore field when they achieve full operating capacity, said a top official.

"We are now witnessing their completion and operation," Ali Kardor, managing director of National Iranian Oil Company quoted as saying by Iran Daily, which cited Iran Petroleum.

Iran Petroleum put South Pars' current gas output at 540 million cu m per day — up from 280 million cu m per day in 2013, according to a report by Shana.

Total development costs for phases 17-21 was around $18 billion. Nearly $7 billion for the combined phases 17 and 18, $5.5 billion for phase 19 and $5.3 billion for the combined phases 20 and 21, Kardor said.

Each new South Pars phase would raise Iran's GDP by one per cent, Kardor estimated, adding that incremental South Pars gas supplies would displace liquid fuels, allowing the country's oil exports to rise.

"Any delay in bringing these phases into operation means funnelling profits to Qatar's market," he said.