The need for special gasolines for racing has grown over the past 40+ years as engine technology has evolved and engine efficiency have improved. What started out as supplying service station gasoline to early stock car racing competitors in the National Association for Stock Car Automobile Racing, Inc. (NASCAR) has grown into supplying a specialized racing gasoline for the very sophisticated racing engines used in stock car racing as we know it today.In 1951 the Pure Oil Company, which merged with the Union Oil Company of California (now Unocal) in 1965, began supplying gasoline for stock car racing sanctioned by NASCAR in the southeastern United States. Today, Unocal continues to provide gasoline to NASCAR, but it is a significantly different product than in the 1950's.In the early years, compression ratios and horsepower output were relatively low (average of 7:1 and 101 for the 1951 model year) and octane demand was satisfied by service station gasoline. As horsepower and compression ratios increased, a demand for special blends of gasoline tailored for racing became apparent. That need was met by changing the Reid Vapor Pressure to reduce the tendency for fuel pump vapor lock.As stock car racing grew, so did the need for special blends of gasoline with increased octane quality. When engine displacement increased in the 1960's, an additional demand for high octane quality was created. That need was also met with additional octane quality to satisfy large cylinder bores, high engine output, hemispherical combustion chambers, and higher compression ratios, as racing speeds increased and new superspeedways were built where 200 mph was exceeded on a closed course.The computer age of the 1980's brought about advanced techniques for commercial gasoline blending. These new techniques were used to update racing gasoline blending and to optimize the use of high octane quality blending stocks to stay ahead of improved racing engine technology.During this era, Unocal engineers developed a procedure to evaluate the effectiveness of high octane quality gasoline in real world racing engines on engine dynamometers. The procedure was based on the Modified Uniontown Technique originally developed to determine Road Octane Numbers (RdON). RdON is the anti-knock performance of the fuel when subjected to the real conditions found in multi-cylinder engines in automobiles. This test work was done using a racing engine on a high speed engine dynamometer to eliminate the variables found in vehicle testing on a chassis dynamometer.The 1990's have brought more sophistication to racing and the need to provide consistently high performance gasoline as racing evolves. The fuel and lubricant products provided for racing have continued to satisfy the demands of the engine builders for the past 40+ years.The paper will provide the technical methods used to develop racing gasolines beginning in the 1950's up to the present. Variables evaluated throughout the years include refinery blending stocks, anti-knock additives and their concentrations, and surface ignition control additives. Since the 1960's, state of the art racing engines have been the test tools used in these evaluations. Data presented in the paper will include the test methods as well as the results of the testing.