A Coordinating Research Council, Inc. (CRC) cooperative program was conducted to determine the difference in octane requirements between technical raters and “customers.” The trained raters used the CRC E-15 procedure to determine the octane requirement of the vehicles while the customers' perception and objection to knock were determined through the use of a questionnaire. The results showed that the customers' objections and perceptions were overwhelmingly based on knock, rather than acceleration performance or after-run. The difference between the technical and customer octane requirement at the midpoint satisfaction level was 3.8 (R+M)/2 octane numbers using the population comparison and 4.1 (R+M)/2 octane numbers using the distribution of delta analysis. The statistical analysis of the database also showed that the differences between customer objection and perception levels were generally small (less than or equal to 1 (R+M)/2 octane number). Knock sensors were found to have significant effect on the difference between the technical and customer ratings; this effect may be due to a decrease in customer awareness when knock sensors were present. This study and the previous studies found the customer/rater deltas increase as the technical ratings increase.