The traditional explanation for dual-task interference is that tasks compete for scarce processing resources. Another possible explanation is that the outcome of the processing required for one task conflicts with the processing required for the other task. To explore the contribution of outcome conflict to task interference, this paper describes two experiments with college undergraduates that manipulate the relatedness of tasks. Experiment 1 found that the difficulty of the individual tasks is not the only determinant of how much they will interfere when combined, and that there must be substantial interactions between processes carrying out the two tasks. Experiment 2 found that although between-category search was more efficient than within-category search in single tasks, it was less efficient in dual tasks. There appears to be significant task interactions due to the confusability emerging when the nontargets of one task belong to the same category as the targets of the concurrent task. In addition, the congruence of target presence or absence on the two channels was found to have a sizeable effect. Four potential sources of outcome conflict are discussed. (Author/PN)