Oil not to be replaced anytime soon: Exxon CEO

Alternative fuels will grow but oil will remain the world's leading source of energy for another quarter century, the CEO of America's largest oil and gas company Exxon Mobil Corp. said Wednesday.

Oil will account for about one-third of all energy use in 2040, Rex Tillerson said at the company's annual shareholder meeting.

Natural gas is expected to overtake coal as the second-largest energy source by 2025, and global demand for natural gas will rise by about 65 percent from 2010 to 2040, he predicted.

Exxon's projection echoes the opinions of many industry leaders. Renewable energy is predicted to provide a growing source of energy, but genuine reliance on it would depend on the development of large-scale and cost-effective energy storage. Fossil fuels will remain central to the energy mix given their affordability and the scale of existing infrastructure.

BHP Billiton, an Anglo-Australian multinational mining and petroleum company based in Australia, predicted over 70 percent of the world's energy will still be supplied by oil, gas and coal in 2030. Natural gas is expected to see the strongest growth through wider use in power and transportation.