Google Inc. on Friday said it has expanded a test of an offline advertising program to include more than two-dozen magazines.

Advertisers can bid until Feb. 20 for placement in the publications, which include such titles as Martha Stewart Living, Motor Trend and InformationWeek, published by CMP Media, which also owns TechWeb. Advertisers can bid on full-, half- or quarter-page ads.

As part of the bidding process, Google, based in Mountain View, Calif., is providing circulation and demographic information, along with publication dates for each publication. Advertisers are asked to specify the maximum amount they would be willing to pay for an ad.

Nearly all of Google's revenues are from selling ads that accompany search results. Called contextual advertising, the ads automatically chosen for a page depends on the keywords used by the searcher. Advertisers bid on keywords.

Google, however, is working on diversifying its ad business by extending its network beyond the Web to magazines, newspapers and even radio. The search engine in January agreed to acquire radio-advertising company dMarc Broadcasting in a deal that could be worth more than $1.1 billion over three years. The final cost will depend on the company's performance.

Also in January, Google was running ads in the Chicago Sun-Times, which was the first newspaper to participate in the company's test of offline advertising, which started late last year with several magazines, including Maximum PC, Budget Living and PC Magazine.

The ads in the Sun-Times were similar to Google's text-based AdWords advertising found on search results. The ads included the words "Ads by Google," at the top, and ran in the sports and business sections.