NEW YORK – One out of every two cars will be either a hybrid or some other alternative-fuel vehicle by 2040, Exxon Mobil predicted Thursday.

Hybrids, which rely on both gas and electricity, currently account for less than 1 percent of all vehicles on the world’s roads. They should move into the mainstream as governments boost fuel-efficiency requirements, Exxon said.

Power for those hybrids, along with other vehicles and a growing number of households around the world, will increasingly come from natural gas, nuclear power and renewable energy sources like wind, Exxon said in its annual long-term energy outlook.

But the company also makes clear that oil will remain king of the energy world.

By 2040, 90 percent of the world’s transportation will still run on oil-based fuels, Exxon said. At current demand, Exxon estimated that the world has enough oil to last 100 years.

William Colton, Exxon’s strategic planning chief, said vehicle mileage standards may push people toward battery-powered cars, but the cheapest hybrids will be those that also use gasoline. Plus, petroleum packs a punch that simply cannot be beaten by a battery alone. “One gallon of gasoline has enough energy to recharge an iPhone for almost 20 years,” Colton said.

Analysts have been predicting a rise in sales of hybrid vehicles, especially since the auto industry agreed in July to boost mileage requirements. Those requirements, proposed by the Obama administration, call for doubling the average fuel efficiency of U.S. vehicles to 54.5 miles per gallon by 2025.