An experiment based on Allen's calculus and its transfer to qualitative spatial reasoning, was conducted. Subjects had to find a conclusion X rj Z that was consistent with the given premises X rj Y and Yr2 Z. Implications of the obtained results are discussed with respect to the mental model theory of spa?tial inference. The results support the assumption that there are preferred models when people solve spatial three-term series problems. Although the subjects performed the task surpris?ingly well overall, there were significant differences in error rates between some of the tasks. They are discussed with respect to the subprocesses of model construction, model inspection, validation of the answer, and the interaction of these subprocesses.