Nitrogen bases of Imilor petroleum, soluble in n-pentane, contain cycloalkyl-pyridine, quinoline and benzquinoline derivatives. Benzquinolines in Imilor petroleum have more alkyl substituents than do those in Salym petroleum. Petroleum nitrogen bases, insoluble in n-pentane are characterized by largest molecules and poly-functionality, they are particularly evident concentrates from Upper Salym petroleum. Typical nitrogen bases in Imilor petroleum, show an average molecule in which each fragment contains two to four aromatic rings with some naphthene substitution, with the longest alkyl chain attached to the naphthene ring.