During the fall of 1971, the Coordinating Research Council conducted a test program at Yuma, Arizona, to investigate a drivability test procedure and the effects of fuel volatility on drivability during hot weather (90-100°F). The procedure included evaluation of vapor lock, hot start and run, and traffic driveaway. In phase I, 12 late-model automobiles and two fuel series were evaluated. In phase II, four cars and four raters were used to evaluate repeatability and reproducibility. Traffic driveaway of individual cars was related to fuel volatility but could not be defined by a general volatility factor for all vehicles. Vapor lock, as in the past, was related to front-end volatility. A usable procedure was demonstrated; however, it was shown that for traffic driveaway, the influence of the rater should be reduced.