AbstractMotivated by recents results for the double‐layer on Pt(111), I reexamine the theory of weak adsorption on double‐layer properties, and use it to explore the capacitance at low electrolyte concentrations. Even a very weak adsorption enhances the double layer capacitance, so that it may exceed the value CGC predicted by Gouy‐Chapman theory. A Parsons‐Zobel plot of vs. for the experimental capacity C does not result in a straight line of unit slope, but roughly follows a linear relation with smaller slope. These results are in line with older data on Ag(111), and with the new data on Pt(111).