Almost all WTO dispute panels exceed their statutory time limits. This is often seen to indicate a more general problem for panels to manage their tasks. The time required varies considerably across panels however, suggesting that they do not face the same problems. To shed light on these differences, this paper examines the relationship between the time panels require and features of their tasks. It finds that variables intended to capture quantitative aspects of panel workloads, as well as some complexity aspects, are positively related to the time required. But two factors that should simplify panels' tasks - a large case law, and panelists' experience from serving on earlier panels - do not seem to matter. The results are sensitive to the inclusion of certain disputes however, raising the question of whether these should be viewed as outliers.