Spectroscopic methods of proton and carbon-13 NMR have been applied to the characterization of a number of middle distillate fuels. The chemical composition of the fuels is determined in terms of average structure parameters and hydrocarbon types without previous sample separation. The structural parameters in conjunction with elemental composition, average molecular weight and average carbon chain-length data describe structure features of representative molecular structure, such as the average number of different types of aromatic and paraffinic hydrogens and carbons, average number of aromatic rings and average degree of substitution on an aromatic ring. This type of analysis is useful in visualizing the types of structures that may be present and allows quantitative structural comparisons between the fuels. Comparative characterization of the fuels was also made by their physical properties and well-known physical property correlations.