Olefins are highly nonlinear octane blenders so that standard GC analyses are poor predictors of blend quality. Engine rating is the only way of measuring olefin octane number nonlinearity. It is thus not possible to rapidly assess the quality of the product obtained from an olefin-producing process-stream. An analysis of the kinetics of olefin combustion in terms of mechanisms for depleting active radicals identities hydrogen abstraction from an allylic carbon as a factor that increases resistance to knock. We can use NMR to find the allylic hydrogen fraction in a sample, and we show that this correlates with mixtures of olefins obtained during processing of the typical gaseous products of a cat-cracked stream. This simple application of NMR has the advantages of quantitatively probing octane number on a sound chemical criterion, as well as the fact that it is fast and requires only small amounts of sample so that process optimization for olefin quality on a small-scale microflow reactor can easily be carried out.