An advertising distribution system mediates and distributes advertising opportunities, especially insertions of ads on web pages, according to advertisers' representative targeting profiles. The number and characteristics of future ad impressions is forecast. A portion is allocated to guaranteed-delivery advertiser contracts and the remainder is offered on a spot market. A division between guaranteed and spot market allocations is sought to maximize revenue, taking into account a value associated with meeting the advertisers' representative profiles. The value of representativeness can be inferred from the marginal revenue of a spot market sale, and optionally weighted. The guaranteed and spot market revenues for all possible efficient allocations produces a curve. An operating point on the curve is determined by selecting a weighting factor or selecting a proportion of total revenue that shall be attributable to representativeness.