Resinous components of heavy oil from the Usa oilfield have been studied using a set of instrumental methods. The properties of average molecules of resins and their high- and low-molecular weight nitrogen bases have been presented. It has been found that the structure of the resinous components have moieties linked by ester/ether and sulfide bridges. They are represented by normal and branched alkanes, alkylcyclopentanes, alkylcyclohexanes, mono- and polycyclic aromatic hydrocarbons, benzo- and dibenzothiophenes and their homologs, and aliphatic alcohols and acids. It has been demonstrated that the nitrogen bases are structural units of the resin molecules, rather than their peripheral moieties.