To compare and test the agreement between Reaktoro and PHREEQC, "phreeqc.dat" and "pitzer.dat" were used as databases. For the model implementation in Reaktoro, where the database does not constrain the selection of the thermodynamic models for the aqueous and gas phases, the "DebyeHuckelPHREEQC" and "ActivityModelPitzer" were used as thermodynamic models for the aqueous phase with the "phreeqc.dat" and "pitzer.dat" databases, respectively. For the gas phase, the Peng Robinson model as developed in PHREEQC (i.e., "ActivityModelPengRobinsonPhreeqc") was selected. These models were chosen to ensure consistency, as mixing a thermodynamic database developed for a specific electrolyte model with a different model for activity coefficient estimation may lead to incoherent predictions. Models simulating the solubility of gases from single (i.e., CH4, N2, H2S, O2, CO2, H2) and binary gas systems (CO2-CH4 and CO2-N2) in water and aqueous solutions are implemented in both PHREEQC and Reaktoro. The results from these models are compared and assessed against experimental measurements available in the literature. Within the phreeqc and pitzer databases, some gases are defined as either coupled or decoupled from redox processes. In the former case, the gases, once dissolved, can be reduced/oxidized to other aqueous species. For instance, dissolved nitrogen, N2,(aq), could further evolve to NH 4 + species. These redox processes are deemed to be considerably slower and kinetically driven and, therefore, neglected in this study. Thus, when available, the definition of the gases uncoupled from redox processes is used in the implemented PHREEQC and Reaktoro models.