CRC-Motor activity in the general area of antiknock work is discussed. The early part of the paper presents a general discussion of all the vehicle and single-cylinder engine work being carried out by three Groups within CRC-Motor. The vehicle antiknock work is described, as well as the octane requirement survey work which can indirectly result in vehicle fuel ratings. It is pointed out that the primary purpose of all of the work in CRC-Motor is to provide data for establishing the antiknock requirements of vehicles, the antiknock performance of fuels in these vehicles, and means for understanding why the fuel engine relationship is what it is. The second part of the paper is devoted to the activities of the “Group on xpression for Fuel Knock Ratings.” This group has as its objective the description of the antiknock characteristics of fuels in vehicles in terms that can be expressed from single cylinder tests made in laboratory engines. Laboratory engine tests are not restricted to the standard ASTM techniques. The program so far has been devoted largely to exploration of the relationships between fuel and engine parameters. The program is designed to provide background information which might very well be used as a basis of new ASTM methods having greater significance.