1. A method, comprising: obtaining proposed offer data that request distribution of a first set of advertisements according to first allocation constraints, the first allocation constraints specifying a maximum price that a first advertiser will pay for distribution of the first set of advertisements; obtaining allocation data for a second set of advertisements to which slot inventory are currently allocated, the allocation data specifying: second allocation constraints for the second set of advertisements, the second allocation constraints being indicative of a minimum amount of the slot inventory that must be allocated to the second set of advertisements; and current allocations of the slot inventory to the second set of advertisements, the current allocations indicating that more than the minimum amount of the slot inventory is currently allocated to the second set of advertisements; determining, based on the proposed offer data and the allocation data, that: re-allocation of a portion of the slot inventory from the second set of advertisements to the first set of advertisements will increase total revenue generated by allocation of the slot inventory; and after the re-allocation, at least the minimum amount of the slot inventory will remain allocated to the second set of advertisements; and in response to the determination, re-allocating, in accordance with the first allocation constraints, the portion of the slot inventory from the second set of advertisements to the first set of advertisements, the re-allocation being performed without violating the second allocation constraints.