Oil companies have collectively gathered up rights to more than 6.5 billion gallons of water in preparation for future efforts to extract oil from shale deposits in the Rocky Mountains, according to a new report by a conservation group that opposes such projects.

Western Resource Advocates used public records to determine that energy companies are entitled to billions of gallons of peak river flows a day and that they hold rights to store, in dozens of reservoirs, 1.7 million acre-feet of water, enough water to supply metro Denver for six years.

Industry representatives said they could not confirm the precise numbers in the report, but they said they have substantial holdings of water rights for future oil shale development.

Extracting oil from shale is still in the experimental phase. Companies are trying to overcome technological, environmental and regulatory hurdles, and it is considerably more expensive than conventional drilling. But the potential payoff is huge: The federal government estimates 800 billion barrels of oil, triple the known reserves of Saudi Arabia, lie under the Rocky Mountains.

Oil companies say that new technologies might reduce future water needs, and even if the oil companies use all of their entitlements, there is no risk of the Colorado River drying up. But if oil shale development takes off, it could use the last of Colorado's allotment of the river's flow provided by a 1922 compact among seven U.S. states and Mexico, said Eric Kuhn at the Colorado River Water Conservation District, leaving Denver's booming suburbs high and dry (Stephanie Simon, Wall Street Journal [subscription required], March 19). -- KJH