The Mason-Monchick approximation (MMA) was used to calculate the viscosity cross-section, S(2000), for carbon dioxide using the most recent intermolecular potential surfaces. The MMA values were compared with the results of full classical trajectory calculations. The deviations obtained were small, at worst 3.4% in magnitude and decreasing with increasing temperature. This rather surprising agreement was traced to the cancellation of MMA errors in estimating two terms that enter the viscosity cross-section. Thus, the MMA may not be reliable as a general tool for testing the accuracy of proposed intermolecular surfaces using viscosity data. (C) 2003 Elsevier B.V. All rights reserved.