We show that early-stage evaluation of critical fuel properties of new gasoline or diesel blendstock candidates can be accomplished using small volumes of material ( < 15 mL, compared to the similar to 1 L typically required). The approach utilizes dilution and autoignition resistance via measurement of ignition delay to estimate the octane number or cetane number of a new blendstock. The ignition delay can be converted to a derived cetane number and derived octane number, providing a useful estimate of a critical combustion property. The results were validated against known compounds. Measurement of autoignition is important for evaluating blendstocks derived from biomass, where generating large volumes for initial evaluation may be prohibitively expensive. We have used this approach for several materials identified as having potential biological production pathways. Also, synthetic organic chemistry was employed to produce sufficient quantities of samples for autoignition measurement for those materials with no established biological scale-up route. The materials investigated were isomers of 5,5-dimethyl-2-ethyl-1,3-cyclopentadiene; branched alcohols and ketones; and hydrotreated terpenoid mixtures. Several candidates were identified with favorable fuel properties for either gasoline (derived research octane number greater than 90) or diesel (derived cetane number higher than 40).