Industry executives attending the IHS CERAWeek energy conference in the U.S. city of Houston predicted a bullish future as the week-long summit came to a close Friday. They believe energy remains one of the driving engines of the world economy and still has boundless potential to tap. Energy sources will become more diversified in the next few decades with the development of renewables, but fossil fuels would remain central to the energy mix. Energy demand is not expected to dwindle in the least, instead growing at a substantial rate over the next 20 years. Developing countries, particularly those in Asia, will be the major contributors to that growth. A louder call was voiced at the summit, one of the world's most influential gatherings of industry leaders, for the U.S. government to ease the ban on crude oil export, as a recent shale boom is rapidly lifting the country from a net importer to a net exporter. Executives argue an open market can only benefit the already oil-sufficient nation economically, politically and diplomatically. But there is no sign yet that Washington will loosen its grip on its strategic assets anytime soon. FOSSIL FUEL REMAINS CENTRAL 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. "As we look to 2030 we anticipate over 70 percent of the world's energy will still be supplied by oil, gas and coal. Gas is expected to see the strongest growth through wider use in power and transportation," said Andrew Mackenzie, CEO of BHP Billiton, an Anglo-Australian multinational mining and petroleum company based in Australia and the world's largest mining company. According to a report released by ExxonMobil, natural gas is expected to overtake coal as the second-largest energy source -- only behind oil -- by 2025, and global demand for natural gas will rise by about 65 percent from 2010 to 2040.