Listings are increasing at ResidentialNYC.com eight months after its launch, even though two of the city’s largest brokerage firms are not yet participating.

The free Web site, which is funded by membership fees and is a competitor to the online classified listings of the New York Times, provides access to condos, co-ops, townhouses, and homes for sale and rent.

With 5,000 listings from 75 firms, up from 3,000 listings from 60 firms when it made its debut in September, the site now has about half of all the exclusive listings in Manhattan, though Prudential Douglas Elliman and the Corcoran Group are not involved in the venture.

ResidentialNYC.com is a portal of a lobbying group for the real estate industry, the Real Estate Board of New York.

“We think it’s doing great,” the president of REBNY, Steven Spinola, said. “We knew it was going to take some time to get the message out.”

Rockrose Development Corp. recently agreed to share its listings with the site, Mr. Spinola said, adding that he expects to announce partnerships with other rental companies in the near future.

The Corcoran Group on Monday announced a partnership with PropertyShark.com, a site that gives users access to residential property reports, including sale prices, appraisal values, code violation information, and previous owners.

“We’re always looking at potential partnerships,” the chief executive of the Corcoran Group, Pamela Liebman, said. “The business has shifted to where the Internet is key to being a successful broker.”

But lending its listings to ResidentialNYC.com is not on the horizon for Corcoran, Ms. Liebman said. “We haven’t talked about it in months,” she said. “We’re focusing on Corcoran.com.”

Corcoran’s Web site has about 4 million unique visitors a month, she said.

Prudential Douglas Elliman, which announced in April 2007 that it would not post its listings on ResidentialNYC.com, did not return calls for comment about whether it is considering a partnership with REBNY’s site.

Mr. Spinola said he is optimistic. “I believe that if we keep going forward and continue to increase the traffic, ultimately everyone out there is going to want to be on this Web site,” he said. “The public should not have to search for 75 different Web sites to find a place to live.”

Some kinks still need to be worked out, but faulty listings usually are fixed within 24 hours, Mr. Spinola said. He added that there is sometimes a lag time between closings and the removal of the corresponding listing from REBNY’s site. But ResidentialNYC.com “continues to be the most accurate listing people can look at,” he said.

When it comes to attracting the attention of New York apartment-hunters, ResidentialNYC.com faces stiff competition from the research site StreetEasy.com, in addition to the New York Times site, an associate broker and vice president at JC DeNiro, S. Hunie Kwon, said.

“I’m hearing more and more buyers and sellers using it,” he said of StreetEasy.com, which allows users to compare rent and sale prices and search by neighborhood, building, public school, and other filters.

ResidentialNYC.com has “a great template,” Mr. Kwon said. “I like the presentation. It’s just lacking the big-name players. Until they break through that barrier, it’s going to be difficult.”