Aerodynamic drag is one of the principal factors influencing fuel economy of passenger cars. Techniques are discussed which enable the effect of aerodynamic improvements to be evaluated utilizing computer simulation. Methods are also presented which enable such improvements to be realized.An acceptable drag coefficient of cD = 0.42 can be readily achieved within conventional styling concepts by refining and optimizing body details. “Detail Optimization” can enable gasoline (Diesel) powered vehicles to achieve maximum fuel economy improvements ranging between 4 % (5 %) and 7 % (9 %) above 1977 averages for subcompacts and full sized passenger cars respectively.Contemporary styling concepts placing great emphasis upon aerodynamics enable minimum drag coefficients of cD = 0.32 to be achieved. Application of such concepts and techniques can enable fuel economy improvements of 14 % (20 %) for full sized passenger cars and 11 % (14 %) for subcompacts to be realized.