Report Suggest Ad Costs will Rise Because of Yahoo-Microsoft Partnership (NASDAQ: YHOO) (NASDAQ: MSFT).

A study published on Monday suggested that the prices paid by advertisers to place ads in search engines may rise after Yahoo (NASDAQ: YHOO) and Microsoft (NASDAQ: MSFT) combine their internet search services.

The report, compiled by search-marketing firm GroupM Search, said that advertisers could pay as much as 78% more to buy ads on the combined service compared to what they’re paying to advertise currently on Microsoft’s Bing search engine. The report cited that after an initial three week period, certain keywords will increase by 78%, but that prices may settle at between 13% and 23% above current prices on Bing.

Microsoft and Yahoo announced a partnership last year in hopes of competing against Google (NASDAQ: GOOG) in search. Under the deal, Yahoo’s search engine will be powered by Microsoft’s Bing search technology. The company announced in August that they had combined organic results and are planning on combining their paid-search advertising networks by the Holiday season.

“Anytime you interject change into the auction, you invite pricing pressure,” said GroupM Search Chief Executive Chris Copeland said in a statement. “In this case, we see historical evidence that suggests regardless of the bid tools and the preparation, a period of short-term volatility will exist.”

Microsoft Corporation is engaged in developing, manufacturing, licensing and supporting a range of software products and services for different types of computing devices. Its software products and services include operating systems for personal computers, servers and intelligent devices; server applications for distributed computing environments; information worker productivity applications; business solutions applications; computing applications; software development tools, and video games. It operates in five segments: Windows & Windows Live Division (Windows Division), Server and Tools, Online Services Division, Microsoft Business Division, and Entertainment and Devices Division. It also designs and sells hardware, including the Xbox 360 gaming and entertainment console and accessories, the Zune digital music and entertainment device and accessories, and Microsoft personal computer (PC) hardware products. In December 2009, it acquired Opalis Software Inc.

Shares of MSFT traded up 0.83% during mid-day trading on Monday.