BILLINGS, Mont. (AP) -- Federal regulators are recommending approval of two natural gas pipelines that could sharply increase fuel shipments from the Rockies to population centers in the Midwest and on the West Coast.

Combined, the proposed pipelines would move almost 2 billion cubic feet of natural gas a day -- enough to fuel about 9 million homes. It would amount to a roughly 25 percent increase over current gas exports from Colorado, Wyoming and Utah.

The Federal Energy Regulatory Commission is expected to make a final decision on the Bison and Ruby pipelines by late March.

Recently completed environmental studies said building the pipelines -- each hundreds of miles long -- would have widespread impact, crossing streams and other bodies of water and disturbing thousands of acres of undeveloped land.

Commission staff members concluded the effects were outweighed by the potential economic benefits, including roughly $30 million combined in annual property taxes. They also said the routes chosen for the pipelines were meant to minimize harm to the environment.

Both lines would originate in gas-rich Wyoming, where a history of limited pipeline capacity has discouraged exploration and forced companies to sell fuel at a discount.

To date, the region has played an endless game of catch-up, with gas production always moving faster than pipelines can be built, said Brian Jeffries, executive director of the Wyoming Pipeline Authority.

"This time we might be out in front of it a little bit," Jeffries said. "Perhaps we'll avoid some of those awful discounts we've had in the Rockies."

TransCanada's $610 million, 310-mile Bison pipeline would run from Gillette, Wyo., through southeastern Montana and end in Morton County, N.D. From there, gas from the line would feed into other pipelines serving the MidWest.

El Paso Corp.'s $3 billion Ruby pipeline would run from Opal, Wyo. to Malin, Ore., passing through Utah and Nevada along a 675-mile route.

The Ruby line is intended in part to fill a supply gap as West Coast imports from Canada taper off, said El Paso's Richard Wheatley. He said it could give gas producers in the Rockies new opportunities to get better prices for their fuel.

"It will afford them a more or less straight shot to new markets in the West," Wheatley said.

A third major pipeline in the region, Rockies Express, became fully operational in November.