CHICAGO — Granola bar sales are booming, especially in Los Angeles. Lay's rules the potato chip market, but not in Philadelphia or Baltimore. And Oreos are the top-selling cookie, period.

Those are some of the findings of a study of snack sales over the past year in U.S. supermarkets, compiled by Chicago-based Information Resources Inc.

While the market research firm didn't provide any commentary with the study, the results clearly show granola bars to be the fastest-growing snack category in the nine metropolitan areas where data were compiled.

The study comes with Americans consuming fewer cookies and trying to eat healthier snacks, such as fruit, yogurt, breakfast bars and baked snack crackers, according to Bob Goldin, an analyst at Chicago-based food consultancy Technomic Inc.

"Granola bars is a classic case of a product that people consider to be pretty healthy ... even though a lot of them are a lot like candy bars," he said yesterday.

According to the study, sales of granola bars rose strongly across the board over the 52 weeks ended Oct. 2 and jumped 23.8 percent from a year earlier in the Los Angeles area, where supermarket shoppers shelled out a total of $26.3 million for them. Houston and San Francisco-Oakland were not far behind with increases of 19.2 percent and 19 percent.

Brand-wise, the results show a close competition between Quaker, which had the No. 1 granola bar in five of the nine cities, and Nature Valley, which "won" in the other four.

Breakfast bars also have been selling well, up double-digit percentages in Houston and Miami-Fort Lauderdale — where shoppers in both markets opted most often for Kellogg's Nutri-Grain Bars — and more modestly elsewhere.

The IRI data show that longtime brand juggernauts such as Oreos, Ritz, Lay's and Doritos continue to be the No. 1-selling cookie, cracker, potato chip and tortilla chip, respectively.