Marketers like Kraft, Wal-Mart and Coke may stop buying ads in magazines if they don't get guarantees on each issue's circulation, reports Ad Age.

Media buyers have long made do with figures on a magazine's average paid circulation instead of guarantees on individual issue circulation. But MediaVest, a media buying giant that bought $900 million in ads for its clients last year, is now making issue-specific guarantees a reality.

The new demands for better metrics can be attributed to the evolution of web metrics and consequent instant-accountability curve, in addition to the myriad of media options now available to marketers.