Search titans could compete on price.

On the surface, Microsoft's $44 billion offer to acquire Yahoo! seems to simplify the US search market share race.

The combined firm would be second in online ad revenues to No.1 Google, and ahead of AOL. In 2007, Google rang up nearly $6 billion, while Yahoo! had about $3.4 billion and MSN had $1.4 billion net revenues.

The top four portals totaled $12.2 billion in online ad revenue for the year. eMarketer's projections put this at more than half of the $21.4 billion market total.

For search ads in particular, Microsoft-Yahoo! would have roughly 18% market share of the search-based ad market, compared with 75% for Google, according to Sandeep Aggarwal, analyst at Oppenheimer & Co., as cited in a Wired article.

eMarketer put search advertising spending at more than $8.6 billion in 2007.

Read more - eMarketer