Yahoo Inc. is releasing more-detailed plans for an online-ad system aimed at increasing revenue from graphical display advertising, such as banner ads.

The effort is a bet that advertisers and Web publishers will be attracted to buy and sell Internet ads across a range of Yahoo and partner sites through a single system, with standardized means of targeting the ads at groups of consumers. The announcement Monday comes as Yahoo attempts to focus its activities and seeks alternatives to an unsolicited takeover bid by Microsoft Corp.

When released, Yahoo's system is expected to compete with efforts ...