In their drive to build customer loyalty and increase sales, grocery chains across the country are adding fuel centers seemingly as fast as customers can swipe their credit cards at the pumps.

West Des Moines-based Hy-Vee Inc., which already operates gas/convenience stores in front of about 40 of its 216 supermarkets throughout the Midwest, plans to open up to 12 more fuel centers by the end of the year.

“We’re making them part of almost all the stores that we build now,” said Ruth Mitchell, a Hy-Vee spokeswoman, who said a fuel center is planned for the store that West Des Moines officials approved last year for the Interstate 80-35/George M. Mills Civic Parkway interchange.

Hy-Vee opened its first Greater Des Moines fuel center at its 74th Street store in West Des Moines; a second is nearing completion at its Pleasant Hill store and construction on a third is beginning in Indianola.

Gas sales at U.S. supercenters and grocery stores already generate about $11 million in annual sales, a figure that’s expected to double by the end of 2005, according to Oil Price Information Service, a trade publication based in Lakewood, N.J. that follows the gasoline industry.

According to a recent article published online by Progressive Grocer, national and regional supermarket chains have been accelerating their construction of convenience store-gas operations. Idaho-based Albertson’s Inc., for instance, plans to add 70 additional fuel centers this year, on its way toward a goal of having 500 centers operational within the next five years.

Additionally, big-box retailers such as Target Corp. and Home Depot Inc. may soon join the ranks of Wal-Mart Stores Inc., which already operates about 600 fuel centers nationwide.

Not all grocery chains are jumping into the fuel business, however. Officials at Boone-based Fareway Stores Inc. say they have no plans to offer gas. The chain operates 85 stores, nearly all of them located in Iowa.

“We stay with what we know, which is choice meat and prime produce,” said Bob Cramer, Fareway’s president and chief operating officer. “We continue to do what we do well and what we have done for 65 years. There’s an old saying, ‘You pay dearly for the price of experience,’ and I don’t know anything about the gas business.”

Hy-Vee, which Mitchell said has a “full plate” of new store projects under way, has not yet announced a construction date for the new West Des Moines supermarket.