Google's eye-popping success in making its search engine an attractive advertising platform has prompted many companies to try their luck in this space.

Because of the stranglehold Google and a few others have on the general-purpose search-engine market, new entrants have created vertical search engines. Unlike their general-purpose cousins, such as the ones run by Google and Yahoo Inc., vertical search engines contain information in their indexes about a specific topic.

Consequently, they are aimed only at people interested in a particular area, and deliver a narrow and very focused audience to the companies that advertise on them. For example, there are search engines for veterinarians, doctors, patients, job seekers, house hunters, recruiters, travelers and corporate purchasers.

As an advertising vehicle, Indeed.com, a jobs search engine, caters to recruiters and providers of online education or training, says Paul Forster, chief executive officer (CEO), who co-founded the company in 2004.

"Advertising on vertical search engines is all about fishing where the fish are. You as a marketer need to go where the target group you're trying to reach is," says Scott Virkler, vice president of business development at GlobalSpec, which links buyers and sellers of electrical, mechanical and optical products and has been around since 1996.

After a company finds a vertical search engine appropriate for its business category, it should determine whether advertising in it can generate attractively priced customer leads for the company, says Jupiter Research analyst Gary Stein. "For many marketers, a vertical search engine makes a lot of sense," Stein says.

Advertisers should also determine the quality of the engines targeting their industries, by inquiring about their index size and determining how useful they are to users, Stein says. "If it's got good data in a large index, then you can say it's a viable business and know your customers will go to that search engine," Stein says.

Experts generally agree that vertical search isn't a passing fancy, but rather a segment of the search market with a high potential for growth. "I don't think it's a fad," says Greg Sterling, an analyst with The Kelsey Group. "The general Web search market is pretty much locked up, so vertical search is where the opportunity to create something competitive is."

Dave Hills is so sure that vertical is the natural evolution and future of search that after he took over as CEO of LookSmart in late 2004, the company launched 181 vertical search sites.

Hills, a veteran of the broadcast industry, is convinced that just as radio, print and TV splintered into myriad outlets targeting niche audiences, the same will happen in search. "The way I view vertical search is that if Google is going to be CBS, I want to be Turner Broadcasting," Hills says.

In a vertical search engine, a company can run an ad that is different from the one it runs on Google, in the same way that a company runs different TV ads on NBC and MTV, Hills says.

Others agree. "It would be as if a print advertiser said 'Gee, The Wall Street Journal reaches all business people in the U.S., so why do I need to advertise in other business publications?' But the truth is it does work to advertise elsewhere," says Dan Savage, CEO of SourceTool.com, a business-to-business search engine designed to link buyers and suppliers.

Vertical search hasn't escaped the radar of Google, Yahoo and the other leaders in general Web search. They all let users search through local business directories and provide driving directions and maps. Some have job engines. Others provide different levels of multimedia content search. But these search engines aren't generally considered to go deep enough into specific areas, which is where others are finding the opportunity.

However, that could change, The Kelsey Group's Sterling says, adding that he's seeing Google and others taking concrete steps to provide more useful vertical search services.