Computer users can type car-related queries into a search engine such as Google. Searches can be general ("cars") -- or specific ("used Toyota Camry"). A results page appears, linking a user to Web sites related to the search.

Advertisers' paid links to their sites appear on the top or right side of the results page. Users can choose to click on those sites to pursue searches.

Typically, a results page on the Yahoo! search engine includes three sponsored sites at the top and 12 links to the right of the main search listings.

The MSN engine generally offers two or three sponsored listings at the top of the page and five or six on the right side. Google displays its sponsored links on the right side of the results page.

A Google search last week for the key word "trucks" displayed sponsored links to Hyundai and Mercury.