Yahoo may have several more reasons to adopt Microsoft's Bing.com to power its search engine. A study by the search advertising network Chitika suggests people who land on sites from organic search results via Bing are 55% more likely to click on an ad, compared with arriving on the site from Google.

Analyzing click-through rates from 32 million ad impressions across a network of more than 50,000 sites during seven days in July, Chitika found that people finding their way to sites from Bing clicked on ads 1.5% on average, compared with 0.97 percent for Google, and 1.24% for Yahoo. About 200 million unique Internet users come through the Chitika network monthly.

Google racked up about 26.9 million impressions on 260,518 clicks, compared with Yahoo's 3.2 million on 39,008 clicks, and Bing's 2.2 million on 33,558 clicks, according to Dan Ruby, director of marketing at Chitika.

Although Chitika's numbers may suggest higher click-through ad rates on Bing, compared with other search engines, Microsoft has "a lot of work to do to retain these people," Ruby says. "Many of these consumers are influenced by ads. What if Google starts a large ad campaign? Will they switch back to Google?

It has been suggested by industry experts, such as behavioral targeting expert Jeff Hirsch, AudienceScience CEO, that niche search engines will play a more vital role for advertisers looking to connect with consumers. This could explain Microsoft's higher click-through rates. It has long been believed that less -- yet better targeted -- ads served up to consumers could produce higher conversion rates.

Take, for example, Microsoft's focus on retail and travel. "There's room for vertical search engines that focus on specific things, such as safety for young people," Hirsch says, but whether that's satisfied by one or multiple search engine remains unknown.

Choice creates ad pricing opportunities for advertisers, which supply and demand should dictate, Hirsch says.

Depending on the company analyzing search engine market share, numbers fluctuate slightly. Net Applications estimates that Google held 81.22% search engine market share in June, followed by Yahoo at 9.21% and Microsoft's Bing at 5.31% and MSN Live at 0.66%. July numbers are scheduled for release Aug. 1.

Compare Net Application numbers with Hitwise, the Experian company tracking Internet trends, and Bing's market share dips to 5.25% in June. That number includes MSN Search and Live.com, and is slightly down from 5.64% in May.

And while Google took the No. 1 spot and YouTube came in at No. 3 in the Alexa's Top 500 sites on the Web, Microsoft's MSN followed at No. 6, Microsoft.com at No. 17, and Bing.com at No. 20.

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