DENVER (AP) - An oil and gas advocacy group says Colorado has billions of dollars worth of petroleum still in the ground and warns that taxpayers could face huge compensation claims if voters ban drilling this fall.

The Colorado Alliance of Mineral and Royalty Owners said Tuesday its members could file claims under the "takings" clause in the U.S. Constitution if new rules keep them from collecting the value of their rights.

At least five oil and gas measures have been proposed for Colorado's November ballot, but none appear to impose an outright drilling ban.

One would increase the minimum distance between new wells and occupied buildings to 2,500 feet (about 760 meters), from the current 500 feet (150 meters).

Supporters have until August to submit 98,500 signatures to get the measure on the ballot.