Abstract: Advertisements can be paired based on their context to achieve increased advertising effectiveness that might not be able to be achieved without the pairing. The advertisements can be paired based on a user's preferred context, which includes an attribute of one of the advertisements. For example, a conditional advertisement can be paired with a scheduled advertisement based on an industry type, the length of the other advertisement, or some other characteristic. Each characteristic can be given a weight, to aid in pairing determinations. The effectiveness of the pairing can be tracked, and the context can be iteratively modified based on the measured effectiveness of the advertising campaign. Pairing can be performed without identifying other advertisers, even though weighting factors may take a sponsor's identity into account. Pairing can be constrained by a master schedule and by a maximum allowed number of conditional spots.