Measurements are reported on changes in the efficiency of the electrochemical oxidation of formic acid that were caused by varying the overall "anion adsorption strength". The adsorption strength was varied by changing the fractions of sulfuric acid and perchloric acid in the electrolyte. It was found within certain conditions that, given two solutions, formic acid oxidation is more efficient in the solution with the larger overall expected anion adsorption strength. The result was found within two very different concentration ranges for sulfuric acid and perchloric acid, and it was obtained in both current- and potential-control experiments. From past experimental results and theoretical considerations, a larger anion adsorption strength would be predicted to cause the oxidation reaction to be less efficient.