World energy demand will grow 30 percent by 2040 when global economic output is expected to more than double and world population would grow to nearly 9 billion, Exxon Mobil said Thursday. However, the growth \"will slow as economies mature, efficiency gains accelerate and population growth moderates,\" Exxon Mobil, the Texas-based largest publicly traded global oil and gas firm said in its newly-released annual energy outlook. As energy use in OECD nations will remain essentially flat, non-OECD energy demand will grow by close to 60 percent, according to it. The single biggest driver of energy demand growth will be electricity, as electricity generation is predicted to account for more than 40 percent of global energy consumption by 2040, the company said. Exxon Mobil predicted that oil, gas and coal will continue to be the most widely used fuels, making up about 80 percent of total energy consumption in 2040. The company also said natural gas use will grow fast to overtake coal as the world\'s second largest energy source by 2025. It also expects hybrid vehicles to have a significant impact on energy use, and predicted that by 2040 hybrids will account for 40 percent of all light-duty vehicles on the road.