Performance evaluation studies were carried out for desalination processes that are based on the humidification/dehumidification principle with different carrier gases through modeling and simulation techniques. The main parameters that measure the performance of these systems are the heat and mass transfer coefficients that determine the humidification and dehumidification rates. The carrier gas properties and geometrical configuration of the unit influence these coefficients. The carrier gas is circulated in these systems by natural convection, which is influenced by type of carrier gas employed, degree of saturation of carrier gas and difference in hot/cold or top/bottom temperatures. Different carrier gases besides air were used in the performance evaluation: hydrogen, helium, neon, nitrogen, oxygen, argon and carbon dioxide. It was found that hydrogen and helium give much better heat flux than air, while argon and carbon dioxide give much better mass flux. Carbon dioxide is recommended as a carrier gas in desalination units that are based on the humidification/dehumidification principle taking into account both the heat and mass fluxes evaluated in them.