Strontium and barium were reacted with water vapor and the kinetics determined in the temperature range 40°–66°C for water vapor pressures from 17.5 to 92.5 mm Hg. The stoichiometry varied according to the reaction conditions. For the strontium reactions the products were and . For vapor pressures below 44 mm the products of the barium reactions were and while for pressures above 44 mm they were and .Manometric and gravimetric methods were employed in the kinetic studies. Both the Sr and lower vapor pressure Ba reactions followed the parabolic rate law. At higher pressures the Ba reaction followed a linear law. An activation energy of was found for the Sr reactions. The activation energy for the Ba reactions was found to depend on reaction conditions.Higher temperature studies of the reactions between water vapor and Sr, Ba, and Ca indicated that in certain temperature ranges above 100°C completely protective coatings were formed similar to those observed in the oxidation of Al or Cr.