Hydrogen, oxygen, and hydrogen peroxide have been measured downstream of an atmospheric pressure humid argon dielectric barrier discharge. The yield of the three species was studied as a function of the discharge power and gas flow rate. Hydrogen peroxide was measured after dissolution into water downstream of the discharge, while hydrogen and oxygen were measured in the gas phase. The production rates of both hydrogen and oxygen were found to be at least one order of magnitude greater than that of hydrogen peroxide. In all cases, the molar rate of molecular hydrogen production was more than twice that of molecular oxygen. At various total gas flow rate, and over a range of energy density of 0 to 1500 J/L, the concentration of hydrogen found at the reactor outlet varied from 0 to 1000 ppm, while oxygen reached a maximum concentration of about 400 ppm. The corresponding concentration of hydrogen peroxide that was calculated to have been in the reactor outlet gas did not exceed 11 ppm. Mechanisms for this system based on experiments and a numerical model are presented. The results of experiments on the use of post-discharge effluent gas of humid argon plasma for sterilization purposes (inactivation of E. Coli) bacteria are also presented and discussed in relation to the results of the chemical measurements and simulations.