Abstract: A network based advertisement system includes an advertisement admission system configured to receive target values that belong to different target categories and to generate a search query associated with the target values and target categories. The system includes a supply forecasting system configured to select sample opportunities that match the search query from a store of opportunities. The advertisement admission system then determines one or more target value combinations. Each target value combination includes at least one target value from each of the different target categories. Then, the advertisement admission system determines a number of available opportunities represented by the sample opportunities that match the one or more target value combinations.