Abstract: A new technique to measure corrosion rates in naphthenic crudes in a high temperature environment has been designed using a gallium phosphate (GAPO) crystal microbalance. The technique is highly sensitive and can measure instantaneous corrosion rates. Due to the high temperature stability of the GAPO crystals, this technique can be used to measure in the laboratory dynamic naphthenic acid corrosion rates of iron at the high temperatures that are prevalent in various locations in oil and gas production and refining facilities, therefore opening a new and more accurate method to study naphthenic corrosion.