The United States' energy self-sufficiency dream will become a reality by 2020, according to Rex Tillerson, CEO of the world's largest publicly traded oil company Exxon Mobil.

"I think it is realistic that the U.S. could be energy self-sufficient by the end of this decade," Tillerson told CNBC on Thursday. "We're already the world's largest natural gas producer (and)last year crude oil production surpassed levels not seen since the 1980s," he said. The U.S. is expected to surpass Saudi Arabia to become the world's top oil producer by 2016, the International Energy Agency (IEA) predicted in November, driven by a boom in the nation's shale oil output.

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In October 2013, U.S. domestic crude oil production exceeded imports for the first time in almost two decades, according to the Energy Information Administration (EIA).

China's huge shale opportunity According to Tillerson, China's shale reserves could be even bigger than those in the U.S., but complicated underground geology presents challenges. "By every geological assessment that I've ever seen, they are larger than the U.S. However there are a number of attributes in China's shale gas reserves that make them particularly challenging," he said.