Yahoo will begin to deliver Google search ads in its own search results pages, as part of a limited test on in the US.

The test is expected to last around two weeks and will be limited to roughly 3% of Yahoo search queries. It is specifically for Google’s AdSense for Search service, so Yahoo would be acting as one of the Web publishers that carry PPC text ads from Google.

Yahoo was keen to stress that the announcement does not mean that it has a long term agreement with Google:

“Yahoo!’s board of directors is exploring strategic alternatives to maximize stockholder value, including exploration of potential commercial business arrangements.”

“The Company noted that the testing does not necessarily mean that Yahoo! will join the AdSense for Search program or that any further commercial relationship with Google will result. The Company further stated that it would not comment on the nature or timing of any potential relationship.”

The trial may suggest that Yahoo is looking at alternatives to a merger with Microsoft, which is still waiting for an answer offer its bid for the company.

Microsoft, however, seems worried about the potential prospect of a Yahoo-Google partnership. According to Microsoft’s general counsel Brad Smith:

“Any definitive agreement between Yahoo and Google would consolidate over 90 percent of the search advertising market in Google’s hands. This would make the market far less competitive, in sharp contrast to our own proposal to acquire Yahoo.”