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.
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.
"Most of these formations are buried much deeper than they are in America. Many of them are in remote areas where there isn't infrastructure to support their development and some in areas where there isn't a lot of water available," he added. Shale gas is extracted by a high-volume hydraulicfracturing (fracking) process that requires large volumes of water.
(Read more: How the US shale gas boom could derail China)
There is no doubt that China will develop a portion of its shale gas reserves, but how much of the large endowment will be developed is difficult to judge, said Tillerson.
Exxon Mobil has partnered with a domestic state oil firm to study to test shale potential in China. However, Tillerson says the company is in the early stages of evaluation.
"Various companies are working with Chinese national oil companies to understand how productive these shale resources will be, what kind of cost would be required to develop them and what kind of infrastructure build out is going to be required,"he said.
(Read more: US to be top oil producer for only four years)
"So it's really a question of pace, and I think it's going to be smaller at the front, and when some of these questions are answered, I think the pace will pick up quite rapidly," he added.
—By CNBC's Ansuya Harjani. Follow her on Twitter: @Ansuya_H