Trained raters determined octane requirements of 248 late model cars using the CRC E-15 Technique and a new method simulating customer-type accelerations called the “Supplemental Technique.” These requirements were compared with those reported by “customers” (car owners). The findings from this program substantiate results from a similar study made in 1975.The differences between the customer and rater requirements at the 50th percentiles were 1.9 Research Octane Number (RON) at E-15 part-throttle and 5.6 RON at E-15 maximum octane requirement conditions. With the Supplemental Technique, the difference was about 4 RON. Five percent of the customers objected to knock when using fuel matching rater requirements, 13 percent when using fuel 2 RON lower and 51 percent when using fuel 6 RON lower.Customer requirements were obtained twice, first with a questionnaire in which knock was not mentioned and then with one which posed direct questions regarding knock. Results were the same with both questionnaires.