Producing hydrogen via sound waves offers a tremendous opportunity for generating an energy carrier in an environmentally-friendly manner. The open literature lacks research studies concerning the effect of the dissolved gases on the ultrasonic hydrogen production process (sonohydrogen). Therefore, in this work, the effect of diluting different dissolved gases on the performance of the sonohydrogen process is studied. The present reaction kinetics mechanism consists of 19 reversible chemical reactions taking place inside the acoustic cavitation micro-bubble and is solved computationally. The results reveal that the dissolved gases have a significant effect on the chemical mechanism of the water vapor dissociation. The present study shows that using carbon dioxide as a dissolved gas within the sonohydrogen process enhances the hydrogen production rate. Two different bubble compositions are investigated; H2O/O-2 and H2O/CO2 bubbles. In the case of the H2O/O-2 bubble, the energy efficiency is calculated, and its value ranges between 1.05 and 1.63 mu mol/kWh, depending on the bubble's temperature. However, in the case of the H2O/CO2 bubble, the hydrogen production shows a considerable improvement with energy efficiency in the range 22.26-34.98 mu mol/kWh. This is due to the lower thermal conductivity, higher heat capacity, and lower thermal diffusivity of the composition of water vapor and carbon dioxide. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.