The efficient allocation of advertisements, also known as creatives, on one or more web sites is provided for while ensuring that guarantees to advertisers are honored. In one embodiment, a linear program solver allocates creatives to advertising slots according to an optimizing function designed to maximize revenue for the site. The linear program solver takes as input a set of creatives, creative performance data, constraints, and slot identifiers. The output of the linear program solver is an optimized schedule not violative of any of the input constraints.