The paper reports results of a study of non-equilibrium effects in the vaporization of multicomponent fuel droplets. The effect of diffusional limitations on vaporization was studied for model systems consisting of n-dodecane doped with pyridine, quinoline, or acridine, which are amendable to both theoretical and experimental study. The model systems were selected to show the effect of non-equilibrium vaporization on nitrogen evolution for the cases in which the nitrogen dopant had a volatility higher than (pyridine), about equal to (quinoline), and lower than (acridine) that of the n-dodecane fuel. Experiments performed on 150-micrometer droplet arrays of real fuel oils revealed non-equilibrium evolution of nitrogenous components. The nitrogen of petroleum residual fuels is usually found to have concentrated in the high boiling and asphaltene fractions. The interplay between volatility and mass transfer effects was shown to be directly responsible for the effects observed in fuel oils by a similar set of model fuel experiments using the doped n-dodecane. Although the model has been applied to a binary system, in this instance, there is no practical distinction between the described processes and those to be found in complex fuels. The only obstacle to the prediction of species evolution from a real fuel is the lack of detailed information on fuel composition and material properties in complex mixtures.