An experimental investigation of the combustion times for nominally 5-μm aluminum particles in water vapor at high temperatures and pressures is presented. The University of Illinois at Urbana-Champaign heterogeneous shock tube facility was used to independently vary the ambient temperature (>2300K), pressure (4-20atm) and composition of water vapor in argon diluent (20-100%) and to observe the combustion of Al particles behind a reflected shock. Burn times were calculated based upon light emission from bands of AlO, an aluminum combustion intermediate. Because the light signals with H 2O as an oxidizer showed longer burn times and more irregular peaks than those found when using O2 or CO2 as an oxidizer, different schemes for calculating burn time based upon intensity cutoff and cumulative intensity thresholds were attempted. The 10-90% area threshold method of burn time was selected and used to report data. A parametric study of the conditions shows that burn time decreases with composition at a faster rate than predicted by diffusion limited theory or the Beckstead correlation. The temperature dependence on burn time is negligible beyond 2500K. A burn time that increased with pressure was an unanticipated result. A correlation is presented for the burn time as a function of these parameters.