HOUSTON -- The United States could be pumping almost 3 million barrels of crude per day by 2020 from tight shale formations that are just beginning to be explored, a top energy economist predicted today.

But whether the United States achieves that level of production -- on top of the 5.5 million or so barrels of domestic crude pumped last year -- depends on economics and the attitudes of regulators, said Daniel Yergin, the Pulitzer Prize-winning author of "The Prize" and chairman of the energy consultancy IHS Cambridge Energy Research Associates (IHS CERA).

Globally, "we see a much larger resource base than other people see," Yergin told the annual World Energy Council business forum here.

Shale or tight oil extraction in the United States, he said, is "kind of the hottest story right now."

By the end of this year, companies will use hydraulic fracturing to produce about 900,000 barrels of oil per day from shale and other difficult-to-extract oil formations. That number could expand by another 2 million barrels per day by 2020, he said.

But Yergin cautioned that such a rapid upswing in production depends entirely on not only the price of a barrel of oil but how willing the federal and state regulators are to allow it to happen. For example, he said, in the Rocky Mountain West, IHS CERA estimates that drilling-permitting rates are 6 percent of where they were four years ago.

"That's not geology, that's politics," he said.

While the global demand for energy will grow substantially from emerging market economies, rapidly moving developments suggest crude and natural gas supplies will also grow substantially, he said.

Argentina, Poland, Ukraine and even China are now seen as following the United States in shale oil and gas development. France's ban on hydraulic fracturing and the emotional debate over the practice in the United States, however, show that the industry will still face challenges in surmounting environmental concerns both domestically and abroad.

Most energy supply growth will happen in the Western Hemisphere, Yergin and other industry experts predict.

Yergin's firm says Brazil could be pumping up to 5 million barrels per day by 2020 if oil prices stay strong and developers and policymakers there support it. That production represents twice what Venezuela produces now, meaning Brazil would replace that oil-rich nation as the energy powerhouse in South America.

Meanwhile, IHS CERA sees Canadian oil sands production expanding to 3 million barrels per day in the coming years, about double what Libya pumped before its civil war.

"Imports to the Western Hemisphere from the East will probably be much lower than they now are," Yergin said.