An advertisement impression distribution system is programmed to generate an allocation plan for serving a number of advertisement impressions changeable as a result of one or more events, the allocation plan to allocate a first portion of advertisement impressions to satisfy guaranteed demand and a second portion of advertisement impressions to satisfy non-guaranteed demand. The system includes an optimizer programmed to establish a relationship between the first portion of advertisement impressions and the second portion of advertisement impressions, the relationship defining a range of possible proportions of allocation of the first portion of advertisement impressions and the second portion of advertisement impressions; and to impose at least one objective on the relationship including moderating an increase in the number of advertisement impressions available for allocation to the first and second portions, to minimize a cost associated with reducing a quality of the advertisement impressions as their volume increases. The system outputs the allocation plan to an ad serving module to control serving of the advertisement impressions according to the range of possible proportions of allocation between the first and the second portions.