A combined modeling and experimental study was performed to understand the dependence of the cathodic current delivery capacity on the electrolyte film thickness and cathode size in a galvanic couple. The appropriate cathodic kinetics for the modeling were generated by use of a rotating disk electrode to simulate the electrolyte film thickness. These results provided boundary conditions for a finite element model which calculated the potential distribution along a metallic surface and the associated cathodic current supplied for electrolyte layers of varying thickness. The total cathodic current was then calculated through integration of the current density across the surface. Electrolyte layer domains were delineated by three limits which described, in order of decreasing film thickness, i) transition in exposure condition from full immersion to thick film, ii) the hydrodynamic boundary layer due to natural convection which defined the upper limit of the thin film regime, and iii) the relative dominance of ohmic resistance over mass transport in determining the total current output. This study also showed that for sufficiently thin films, this total current was independent of the size of the cathode and the nature of kinetics at the electrochemical interface, being solely driven by the ohmic resistance in solution. Dissimilar engineering alloys in close proximity and in electrical contact are frequently encountered in the architecture of high-value structural assets in the transportation, aerospace, and marine industries. In service, these structures are often exposed to atmospheric environments, such as sea spray, that result in the formation of a thin electrolyte layer on the surface sufficient to allow the dissimilar alloys to form galvanic couples. Under atmospheric conditions, the electrolyte can also form via deliquescence of salt as either a droplet or a thin film on the alloy surface, leading to the establishment of a corrosion cell. The extent of galvanic corrosion on the anode that results depends on a number of environmental, physicochemical, and geometric variables, which include relative humidity, temperature, electrolyte conductivity, electrolyte film thickness, in addition to the electrochemical kinetics on the alloy surface.1-7 Different exposure conditions can be modeled by varying the thickness of the electrolyte film (also termed the water layer, WL), which in turn affects solution resistance as well as cathodic kinetics, thus having a direct effect on the total cathodic current available to support corrosion of the galvanic system.The effects of the electrolyte film thickness on corrosion rate were recognized initially by Tomashov, 2 who qualitatively identified four regions of WL corresponding to different types of reaction control. As film thickness decreased, a transition from a plateau in corrosion rate when a constant diffusion layer was attained (conditions of full immersion) to cathodically controlled corrosion limited by diffusion of dissolved oxygen to the reaction surface (the corr...