An experimental investigation was undertaken in which transient condensation of steam-air mixtures occurred on one face of a large aluminum block of which all the other faces were insulated. Tests were conducted in a pressure vessel at pressures of up to 650 kPa. The transients were provided by a sudden increase in the vessel pressure from a given value to a much higher value by the introduction of additional steam. Temperature measurements within the block agreed well with results from a finite difference analysis of the condensing surface and block. Visual observation of the condensing surface indicated that the mode of condensation was predominantly dropwise. The dependence of the heat transfer coefficient on time, pressure, severity of the transient, percentage of noncondensables, and the driving temperature difference was studied. The results at the much higher pressures and transient conditions used in this study agreed with observations in the literature of such trends at lower pressures. There was evidence of the occurrence of a buildup of noncondensables at the condensing surface with time.