Perovskite-type catalyst samples LaySr1-yRuxCr1-xO3 (y = 0.7; 0.025 less than or equal to x less than or equal to 0.100), synthesized by the ceramic method, were used in activity measurements in the simultaneous conversion of CO, hydrocarbons (HC), and NOx in the pulse-flame catalyst testing (PFCT) system and synthetic dry gas mixtures. In the presence of water vapor, in the reaction mixture (PFCT system), an unusually high level of CO oxidation and a higher concentration of H-2 detected in the outlet reactor gases, compared to the inlet reactor gases, can be ascribed to a water gas shift reaction. The generated hydrogen, present on the catalyst surface in its dissociated form, could be responsible for the higher NOx conversion under net oxidizing (lean) conditions, which favors ruthenium synthesized catalysts as three-way auto exhaust catalysts.