Denver (AP) Gov. Bill Ritter says the Bush administration is prematurely pushing to develop oil shale in Colorado.

Ritter said Wednesday the president blocked the extension of a provision that effectively banned leases on federal land for commercial oil shale development. The provision expires Tuesday.

Ritter wrote Interior Secretary Dirk Kempthorne a letter saying it's “irresponsible” to press ahead with commercial oil shale leasing now.

Oil shale on public land in Wyoming, Utah and Colorado is believed to contain about 800 billion barrels of recoverable oil.

The technology to squeeze the oil out of the rock is still experimental and commercial production is likely at least a decade off.