A project operated under the auspices of the Canadian Crude Quality Technical Association (CCQTA), examining the correlation between the total acid number (TAN) of Athabasca bitumens and corrosivity, encountered problems in applying the standard method, American Society for Testing and Materials (ASTM) D664. These problems were manifested by poor reproducibilities and resulted in a thorough review of the application of the method to bitumens and heavy oils. Factors considered were asphaltene precipitation, sample size and reagent concentrations, and a correlation to a naphthenic acid extraction method. As a result of this study, modifications to ASTM D664 were suggested, which related to initial sample handling but did not significantly alter the basic test method. Employing these modifications, a small three-laboratory round robin using an Athabasca bitumen with a mean TAN of 3.30 mg of KOH/g yielded a reproducibility of 3% relative standard deviation.