The new-car sales experiment between General Motors and San Jose e-commerce powerhouse eBay begins yesterday in California, and both companies will be closely watching the results ¡ª particularly GM, which is hoping to increase its market share in the state.

"Dealers who are participating see this as a great mechanism to get their products and information out to people where they're doing initial shopping and looking, which is on the Internet," said Dave Barthmuss, western regional spokesman for GM.

The program, announced last month by GM, will involve 225, or 90 percent, of California dealers. Barthmuss said California was selected as the test market for the four-week trial because GM sales in the state have historically been "far below the national average," and its residents are considered tech-savvy.

"It's all about simplifying the car-buying process," Barthmuss said. "It's basically extending the dealers' reach beyond the showrooms and car lots of their brick-and-mortar buildings to the buyers' laptops and shopping in their living rooms."

The new Web site, gm.ebay.com will be available through Sept. 8, and if it's successful, Barthmuss said, GM would like to roll it out nationwide.

GM dealers already sell used and certified pre-owned cars on eBay. And plenty of dealers already negotiate car sales directly with customers over the Internet. But this is a new experiment for the automaker, which has never sold new cars on eBay, and for the first time is making its entire California inventory available to buyers. However, all car sales must go through the participating dealers.

For the next four weeks, consumers will be able to browse a selection of up to 20,000 Chevrolets, Buicks, GMCs and Pontiacs from 2008, 2009 and select 2010 models.