Regional differences in gas trapping between the apex and base of the lung were assessed in excised lungs from male Long-Evans-hooded- rats. The lungs were ventilated with air as they were suspended upright, inverted in saline, or supported upright in saline, and pressure volume curves were recorded for each of the three conditions. The distribution of transpulmonary pressures over which gas trapping occurred was evaluated by statistical analysis. Increasing uniformity of gas trapping was associated with a decreasing standard deviation for the distribution of transpulmonary pressures. The standard deviations for the distribution of transpulmonary pressures under the three conditions of the study were 1.10, 0.63, and 1.57 for the lung in air, inverted in saline, and upright in saline, respectively. The authors conclude that gas trapping in lungs occurs at the base before it occurs at the apex and that gas trapping for lungs inverted in saline is more uniformly distributed from apex to base than gas trapping in lungs either upright in saline or in air.