Sandra Henderson has shopped for groceries at Raley's for 30 years. So what was she doing wheeling a cart into the West Sacramento Wal-Mart Supercenter on Tuesday?

"It's the economy," she said.

Wal-Mart's giant discount stores posted by far the biggest gain in market share of any grocery chain in the four-county capital region through the first half of the year, according to new data from Trade Dimensions Inc., a market research firm.

Meanwhile, West Sacramento-based Raley's, the region's largest supermarket chain, continued to bleed business, according to the report.

Nationwide, conventional supermarkets are losing shoppers to big discounters – a trend that has accelerated as the economy flags and more shoppers feel worried about their financial future.

"Raley's might have very high customer satisfaction, but people still might not come back because they're hedging against (financial) risk," said Ashwin Aravindakshan, a University of California, Davis, professor of marketing.

Nonetheless, the No. 2 local grocer, Safeway, has been adding customers, a performance analysts credited to the chain's big investment in upgrading its stores. Save Mart, the third-largest player in the market, slipped slightly.

Arkansas-based Wal-Mart opened its first Supercenter – a hybrid supermarket and discount store – in the Sacramento region less than three years ago. Today, its five Supercenters own 8.3 percent of the local market, with each store bringing in more than twice the grocery business of an average Safeway or Raley's location, according to Trade Dimension figures.

Wal-Mart spokesman Kevin Loscotoff said the company has plans for three more Supercenters in the region – a new store on Florin Road, an expansion of the existing Folsom Wal-Mart and a new store in Galt.

Wal-Mart has grown to be the nation's largest grocer with a low-prices pitch that has consistently lured shoppers from more service-oriented supermarket chains.

"The customer keeps hearing Wal-Mart has the lowest prices, and then they'll go try 'em once or twice," said George Whalin, who heads Retail Management Consultants in San Marcos. "And if they're willing to put up with that shopping experience, then they'll become a loyal Wal-Mart shopper."

Henderson, a retired day-care provider who lives with her husband in West Sacramento, said she loves the helpful staff at her local Raley's and still prefers to buy her meat and produce there.

But as she looked to cut expenses, she decided to try the new Supercenter and found better prices on staples like cereal and canned goods. And while she doesn't expect to get helped out to her car at Wal-Mart – a service she said Raley's clerks always offer – she's kept coming back.

Nationwide, Supercenter-type stores are gaining about one point of market share annually, while traditional supermarkets are losing share at about the same rate, according to a recent report by the consulting firm Willard Bishop.

Over the past 18 months, Raley's has lost 2.4 percentage points of market share, leaving it with slightly more than a third of the local grocery business. Each share point in our region is worth about $35 million in annual sales.

Bob Reynolds, a grocery consultant based in Moraga, said Raley's has shifted its pricing and advertising strategies frequently in recent years – a sign the company is casting about for a new direction.

"They've tried a lot of different things, which suggests to me that the things they have tried haven't shown startlingly good results," he said.

Raley's disputes the Trade Dimensions figures, but wouldn't provide an alternate measure of the company's trajectory. Unlike most other chains, Raley's doesn't provide Trade Dimensions with data from its own distribution centers, so the market research firm estimates Raley's market share from figures reported by one of the chain's major suppliers.

Spokeswoman Amy Johnston said Raley's is "not experiencing significant changes" in market share.

Safeway's comparative success in the Sacramento region – it picked up 0.4 percentage points over the last 18 months without opening any new stores – is likely the result of recent overhauls to most of the chain's stores, experts said. Safeway's new and remodeled "Lifestyle" stores target higher-end shoppers who don't necessarily choose where to shop based on prices, said John Stanton, a professor of food marketing at Saint Joseph's University in Philadelphia.

"They're saying, 'We're not really going to go after the Wal-Mart customers,' " Stanton said.

Call The Bee's Jim Downing, (916) 321-1065.