Google is the undisputed king of search in the United States.
But who's number two?
Yahoo! has long held that position but Microsoft has been creeping up and may even have leapfrogged the Sunnyvale, California, company in a competition whose goal is to turn more Internet searches into more advertising dollars.
According to The Nielsen Co., Microsoft, led by new Web search engine Bing, overtook Yahoo! for the first time in August to make it the number two search service in the United States.
Another digital tracking company, comScore, disagreed, however, releasing August search share figures just days after Nielsen's that had Yahoo! still firmly in second place.
According to Nielsen, Microsoft's Bing, MSN and Windows Live had a 13.9 percent share of US search volume in August while Yahoo! had a 13.1 percent share.
ComScore, for its part, said Yahoo! accounted for 17.4 percent of the US search market in August and Microsoft 11.1 percent.
Both click-counters agreed that Google remains the dominant player with a 65.1 percent search share in August according to Nielsen and a 65.4 percent share according to comScore.
So who's right -- Nielsen or comScore -- when it comes to the battle for second place?
"I couldn't say one's more accurate than the other," said Danny Sullivan, editor-in-chief of SearchEngineLand.com, a blog devoted to search.
"They've got their own formulas," Sullivan told AFP. "They both have their own ways of measuring exactly what they consider a search to be. For example, comScore will not consider anything that happens on a map page to be a search."
Sullivan said what's important for him is "not whether the numbers are exactly the same but whether or not the trends tend to be the same.
"It's not really 'Is Bing higher than Yahoo!?' but 'Is Bing continuing to close the gap?"
By that measure, Bing has made steady strides since it was launched in June last year, good news for the Redmond, Washington-based company founded by Bill Gates and better known for its ubiquitous software.
"You've got Microsoft, this big, huge powerful tech company, that's been trying to be the number two in search for a long time and they're finally getting there," Sullivan said.
"Part of the reason why you've seen them become successful in this way is that they found a branding (with Bing) that people could understand and latch on to," he said.
"At the same time, you have Yahoo! going through the opposite in some ways," Sullivan said. "They are not positioning their service as what would seem like a competitor to
Microsoft and Yahoo! reached an agreement last year which calls for Bing to eventually power searches at all Yahoo! websites -- although for advertising purposes their search share will continue to be calculated separately.
While Sullivan said it's difficult to precisely determine the value of a percentage point of search, it's a high-stakes game.
"The overall thing is the more that you can grow your share the more likely you're going to be able to tap into some of the millions and billions that Google makes off of ads," he said.
While Google can be expected to rule the search market for the foreseeable future, Sullivan said the Internet titan could see a mild erosion in its share in the short term, the result, ironically, of its own innovation, a product called "Google Instant" unveiled earlier this month.
Google Instant suggests results as a user types a query in the search box and displays them on the same page, eliminating the need to return to the search box if the initial query was unsatisfactory.
"You're only going to register one search under this existing system," Sullivan said. "So what could happen is Google's share could come down."