It’s not a surprise that search advertisers are wary of Yahoo’s deal to have some of its search ads sold by Google. After all, that extra money that Yahoo is hoping to get from the arrangement is coming from somewhere: the pocketbooks of advertisers.

One measure of what sort of effect this will have was published Tuesday morning by SearchIgnite, a company that sells software companies use to manage their search advertising. Its conclusion is that overall, the cost to advertisers of a click from Yahoo’s site will go up by 22 percent if Google sells the ads.

Assuming Microsoft and Carl Icahn can’t derail Yahoo’s plan, its deal with Google is undergoing scrutiny in Washington. It is the subject of a Justice Department inquiry and will also be the topic of a Senate hearing Tuesday.

To compare the actual price its clients paid on Google and Yahoo, SearchIgnite looked at 12 million paid clicks for 15,000 different keywords. It only compared clicks that were for the same position among ads on a Web page: the cost of being listed first on both, for instance, or the cost of being in the third spot.

Interestingly, the price difference varied substantially depending on the sort of word. For the most popular search terms, Yahoo actually was more expensive for advertisers who wanted to be in the first three results. But Google cost more for ads in position four and beyond. Yahoo also costs more for the very first position in searches for brand names.

But where Google costs the most is the vast long tail of less common search terms, the study found. For those terms, even the top spot cost 14 percent more on Google and by the fifth through 10th spot cost 54 percent more. Google, which accounts for more than 70 percent of the search advertising spending measured by SearchIgnite, simply has more advertisers bidding on more terms.

Roger Barnette, President of SearchIgnite, said his firm doesn’t isn’t taking a position how Congress or the Justice Department should react to Yahoo’s deal with Google. But the firm and its clients are concerned about the consolidation of search advertising...