Google announced new options for AdSense publishers, giving them the opportunity to display keyword-based contextual advertising in two new formats.

AdSense publishers can now choose to have the Google text links appear in a 720 x 90 pixel unit or a 300 x 250 inline rectangle unit. Both units can display up to four listings. Previously, AdSense publishers could only choose from a standard 468 x 60 banner and a 120 x 600 skyscraper. The banner units display two listings, the skyscraper four.

The new formats are available to publishers in Google's self-service contextual ad program. Large publishers using AdSense, like Switchboard and Weather.com, have customized units.

The alterations come three weeks after Google backtracked on changes it made to the AdSense units. Google announced that it would add a "related searches" section to units, show white space when it did not have relevant ads, and end the practice of showing public service links on pages where its technology cannot match up the content with an ad. Later the same day, Google retracted the changes after AdSense publishers expressed wide dismay in communications with the company and on industry message boards.

Contextual advertising is widely seen as the next frontier in the search landscape. Google uses its algorithmic search technology to scan content pages and match up keywords to text ads from its 100,000 advertisers. Overture Services has a rival contextual ad program, although it does not offer a self-service option for small publishers.