The world may have 250 years of gas usage at current levels thanks to "unconventional gas" from shale and coal beds, Anne-Sophie Corbeau, senior gas expert at the IEA told BBC News.
Estimates may even be revised upwards.
Studies are underway into newly-recoverable sources, Ms Corbeau said.
But she stressed that the totals were highly uncertain, and depended on price, technology and the accessibility of supplies.
"The gas story is huge," she told BBC News.
"A few years ago the United States was ready to import gas. In 2009 it had become the world's biggest gas producer. This is phenomenal, unbelievable