Opera Mobile and Opera Mini users will start seeing a Google search bar on their browser start pages, based on an agreement between the companies.

Opera made Google the default search engine on both of its mobile browsers on Wednesday. Google replaces Yahoo, which had supplied search for Opera Mini and Opera Mobile based on a deal the companies formed early last year.

While Google has been the default option on Opera's desktop browser for seven years, the mobile browser deal is new.

Without explaining why their year-old deal has ended, Yahoo said it decided to call off the agreement. "Yahoo has elected not to continue its mobile search partnership with Opera at this time," it said in a statement. "Consumers with Opera browsers will continue to have access to Yahoo oneSearch, and as long-standing partners, Opera and Yahoo will continue to work together." OneSearch is Yahoo's search service designed to meet the needs of mobile users.

Opera Mobile is the full browser designed primarily for smartphones. Opera Mini consists of a small downloadable client that works on lower-end phones and that communicates with backend servers operated by Opera or, in some cases, a mobile operator. The servers strip down Web sites for quicker uploading on the phones.

More than 35 million people have downloaded Opera Mini, and they browse more than 1.7 billion Web pages each month, Opera said. Much of that traffic comes from the search function in the browser, Opera said.

Opera Mobile has shipped on 100 million phones from manufacturers including Motorola, Sony Ericsson, and HTC, according to Opera.

The announcement is another indication of the competition among search providers for a foothold in the mobile market. Google and Yahoo have each wracked up wins recently. The search providers hope to find a new and potentially significant revenue stream from mobile advertising as an increasing number of mobile users access the Internet from their devices.

Nokia recently announced that it will feature Google search on some of its phones. Yahoo also recently recorded a significant win by replacing Google as the preferred mobile search provider for T-Mobile in Europe. Yahoo also powers search for AT&T.

This story was updated on February 27, 2008