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. For more on this, see the June issue of Oil and Gas Investor. For a subscription, call 713-260-6441.