Techniques are provided for selecting among the advertisements that are competing for a slot based, at least in part, on an “schedule sequence” that is established for the advertisements. The schedule sequence may, for example, reflect the relative times at which a content provider incurred the delivery obligations associated with the advertisements. For the purpose of establishing the sequence, the date on which an advertisement order is placed may be considered to be the date on which the corresponding delivery obligations are incurred. After the sequence has been established, the position of competing advertisements within the schedule sequence is used as one of the factors for determining which competing ad to place in a slot, where ads nearer the beginning of the sequence (ads with earlier-incurred delivery obligations) are favored over ads that are nearer the end of the sequence (ads with later-incurred delivery obligations).