A group of saturated nonisoprenane dimethyl-branched, alkyl-substituted hydrocarbons of the R-CCCCCC(C)CCC(C)CCCCC-R' type has been found for the first time in crude oils and dispersed organic matter (DOM). Their concentration in the saturated hydrocarbon fractions of crude oils and DOM from the southern part of the Anadyr basin is 1-2 wt % and is well above that of their structural isomers with the closest structure in the same samples. Some ideas about possible sources of these hydrocarbons have been advanced. In the methodological aspect, the simplicity and efficiency of C-13 NMR spectroscopy as applied to searching for previously unidentified alkyl structures in crude oils and DOM have been demonstrated, using as spectral parameters coefficients that determine the dependence of chemical shift on the recording temperature and the concentration of the fraction in the solution.