Asphaltene self-association was modeled in a manner analogous to linear polymerization. The key concept in the model is that asphaltene molecules may contain single or multiple active sites (functional groups) capable of linking with other asphaltenes. Molecules with multiple active sites act as propagators and molecules with single active sites act as terminators in polymerization-like association "reactions". Asphaltenes consist primarily of propagators. Resins, which are known to affect asphaltene association, consist primarily of terminators. The model was tested on existing molar mass data for asphaltenes in different solvents and at different temperatures as well as on new molar mass measurements of mixtures of asphaltene and resins. The model fit the existing experimental data well and predicted the molar mass of asphaltene-resin mixtures to within the accuracy of the measurements.