Tom Pyden, vice president for communications at G.M., explained that the companies had been in long-term discussions and that a partnership was in the works.

He emphasized that G.M. dealers, not the company itself, would list new cars on eBay. “We will not be selling directly to customers,” he said. “We are looking for ways to make it easier for customers to shop and buy our products on their time, on their terms.”

G.M. said the test with eBay would let customers either buy new cars at auction or at a fixed price using eBay’s “Buy It Now” option. But it is unclear whether that fixed price would differ from the manufacturer’s suggested retail price, and how G.M. would react if auction prices were well below that price.

One G.M. dealer said he had already talked with the company about the program and was excited about it.

The dealer, Inder Dosanjh, who owns Dublin Chevrolet outside San Francisco, said listing new cars on eBay would allow his dealership to get

. . . . in front of customers who were doing most of their car shopping on the Internet. He said that would include some people who might not have otherwise considered a G.M. car.