At least one major is explaining why it has "come back" to pursuing more activity onshore the U.S., saying the size of the remaining unconventional gas resources is huge. "And, the required technologies fit our strengths and strategies," says Linda Hubner, onshore exploration manager, EP Americas, for Shell Exploration & Production. "I'd like to give credit to the independents that have opened up these plays. They've fought to make them economically viable," Hubner told attendees at Ziff Energy Group's North American Gas Strategies conference in Houston recently. Recent assessments show that gas resources in unconventional plays are quite large, with the Rockies alone hosting some undiscovered 173 trillion cubic feet, according to the National Petroleum Council's landmark 2003 gas study. Through the 1990s, Shell focused on its leading deepwater Gulf of Mexico position and spent the bulk of its capital and attention developing very large finds there, such as the billion-barrel Mars Field. Now that those projects have been developed and brought to production, the company can turn its attention to onshore unconventional plays, she said. Shell has a tight-gas task force in Houston. It entered the prolific Pinedale Anticline tight-gas play in Wyoming in 2001 by buying privately held McMurry Oil Co. It has taken production there from 15 million cubic feet per day to 200 million in 2005, and it plans to have eight rigs working this year. In 2005, Shell entered the Barnett Shale play and now owns 45,000 acres. It had two rigs drilling at press time but expects to have four by year-end. In the Fayetteville Shale play, it has about 70,000 acres and plans to start drilling in 2007. And, it is participating in a rank wildcat in the Columbia River Basin in Washington state.