The more users search and build up a search history the better the results will become, said Marissa Mayer, who directs Google's consumer Web products.
For example, searching on the word "bass" would show fish-related results for someone who has previously searched on fishing keywords and clicked through to fishing Web sites. However, the "bass" keyword search would show results related to musical instruments if the search history indicated interest in music.
"We need to have a history of the user," Mayer said. "When people first sign up they may not see results right away, but it will build over time."
Consumers must have a Google account to use the service. If they have been using the previous version of personalized search they will automatically be switched to the new version. The service will only be available when the person is signed on to the Google account.
People can sign out of the personalized search service, pause it or remove it through their accounts page, and they can remove items from their search history as well.
The search history feature, launched in April, lets people browse through a timeline of their past Google searches to see the level of activity on any given day, the number of times a user has visited a Web page and the last time it was viewed.
The previous test version of personalized search, launched in March 2004, customized searches only after users selected categories of interest.
The launch is part of a larger effort from Google to allow users to customize their Web experiences. In May, Google unveiled a new feature that lets people set up a personalized Google home page.
Search rival Yahoo also has been working on customization features. In May, Yahoo launched a test version of a personal search feature that lets people archive their search activity and results and share that information with others.