ExxonMobil, the world’s largest listed oil company, has said it will be able to more than double its output in the Permian Basin region of the US and maintain it at that level for decades, in a vote of confidence in the outlook for North American shale production.The company told analysts on Tuesday morning that it could add 350,000 barrels of oil equivalent per day from the Permian region of Texas and New Mexico, thanks to the $6.6bn acquisition of companies from the Bass family announced in January. Its current output in the region is 140,000 b/d.That increase would take shale oil from the Permian and the Bakken formation of North Dakota to 20-25 per cent of Exxon’s total production of crude and related liquids, up from 12 per cent today. It could be sustained on a “multi-decade production plateau”, the company said.Large oil companies including Exxon were left out of the initial boom in US shale gas and oil production, but in recent years it has been working to build up its operations, while its smaller rivals have been under financial strain from the weakness of crude and gas prices. Chevron, the second-largest US oil group, has also been building up its operations in the Permian Basin.