According to a study by Bloomberg New Energy Finance (BNEF) released on Friday, the world’s biggest oil producers are starting to take electric vehicles (EVs) seriously as a long-term threat, Bloomberg reports.

It said OPEC, of which Nigeria is a member, had quintupled its forecast for sales of plug-in EVs (even suggesting sale targets could dampen demand in some parts of Asia as soon as 2018), and oil producers from Exxon Mobil Corp. to BP Plc also revised up their outlooks in the past year. BNEF expects those cars to reduce oil demand 8 million barrels by 2040, more than the current combined production of Iran and Iraq. Growing popularity of EVs increases the risk that oil demand will stagnate in the decades ahead, raising questions about the more than $700 billion a year that’s flowing into fossil-fuel industries.

BNEF expects electric cars to outsell gasoline and diesel models by 2040, reflecting a rapid decline in the cost of lithium-ion battery units that store power for the vehicles. It expects 530 million plug-in cars on the road by 2040, a third of worldwide total number of cars.  The world’s top automakers such as Volvo AB, Tesla and Geely Automobile also have a combined plan to sell 6 million EVs a year by 2025, rising to 8 million in 2030, according to Bloomberg New Energy Finance.