Recent theoretical work has suggested that the air-sea exchange of trace gases such as CO2 can be modified by irreversible thermodynamic coupling phonomena and that the commonly used gas exchange relationships can incorrectly predict the magnitude and, under certain circumstances, the sign of air-sea trace gas fluxes. The physical basis for irreversible thermodynamic effects during air-sea exchange is developed for both the liquid-gas interface and the molecular boundary layers or sublayers adjacent to the interface. The impact of irreversible thermodynamics is shown to differ qualitatively from that predicted by an earlier analysis due to the explicit inclusion in this work of the molecular kinetic layer at the air-water interface. For insoluble trace gases such as CO2 the temperature contrast across the limiting region for air-sea exchange, the aqueous mass sublayer, is not great enough to have a measurable impact on the trace gas distributions, and irreversible effects do not need to be included in empirical air-sea gas exchange relationships. ¿ American Geophysical Union 1995