Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for selecting content items for presentation along with publisher resources. In one aspect, a method includes receiving a request for a content item for presentation at a user device with a publisher resource; receiving, from a content item provider a first selection value for each of a plurality of content items provided by the content item provider; determining, for each of the content items and using accessed distribution parameters, a second selection value distinct from the first selection value; and determining, for each of the content items and independent of a bid corresponding to the content item, a combined selection value based on the first selection value for the content item and the second selection value for the content item.