Nearly 1.6 billion barrels of oil, mostly in the Afghan-Tajik Basin, and about 15.7 trillion cubic feet of natural gas, mainly in the Amu Darya Basin, could be tapped, Afghanistan's Ministry of Mines and Industry and the US Geological Survey said on Tuesday.
Hamid Karzai, the Afghan president, described the estimates as "very positive findings", particularly since the country now imports most of its energy, including electricity.
"Knowing more about our country's petroleum resources will enable us to take steps to develop our energy potential which is crucial for our energy's growth," said Karzai, whose government was created after the US-led invasion in 2001 and later won national elections.
The $2 million assessment, paid for by the independent US Trade and Development Agency, was nearly four years in the making, said Daniel Stein, the agency's regional director for Europe and Eurasia.
The total area assessed was only about one-sixth of the two basins' 200,000 square miles that lie within Afghanistan.
Afghanistan's petroleum reserves were previously thought to hold 88 million barrels of oil and five trillion cubic feet of natural gas, based on Afghan and Soviet estimates for 15 oil and gas fields opened between 1957 and 1984. But just three of those have operated recently.
"There is a significant amount of undiscovered oil in northern Afghanistan," said Patrick Leahy, the US Geological Survey's acting director.
He said the other oilfields were abandoned, or the equipment there was damaged and rocks had filled the wells.
More work remains to assess petroleum reserves, conduct seismic exploration and rehabilitate wells, say government and industry officials.