BP started production at Oman's giant Ghazeer natural gas field in Oman which is set to underpin the company's oil and gas output for years even as it shifts to renewables.

The London-based company said in a statement that Ghazeer, the second phase of development of Block 61, started four months ahead of schedule and below its planned budget.

BP is in the midst of the largest overhaul in its history after CEO Bernard Looney set out a path to rapidly shift BP to renewable power and reduce its oil and gas production by 1 million barrels per day by 2030.

But oil and gas is set to help pay for the shift in the coming decade.

"It is absolutely central for BP because it generates the funding allowing us to invest in new businesses and transform the company," Gordon Birrell, BP head of oil and gas operations, told Reuters.

BP, which wants to sell $25 billion of assets by 2025, is in talks to sell down its stake in Oman, industry sources have told Reuters.

The first phase, Khazzan, was brought online in September 2017. Total production capacity from the block is expected to reach 1.5 billion cubic feet of gas a day and more than 65,000 barrels a day of associated condensate.

BP holds 60 per cent of the Block 61 project, Oman's national oil and gas company 30 per cent and Malaysia's Petronas another 10 per cent.