High-precision mass spectrometric anal., together with model expts. and thermodn. calcns., was used to find and interpret effects of inter- and intramol. stable-isotope order in natural carbonaceous material, including alkanes, resins, asphaltenes, kerogens, graphite, lipids, lignins, carbohydrates, amino acids, and crude oil. These effects, which are well studied for C isotopes, affect the distribution of S isotopes in certain org. compds. Totally different mechanisms, however, account for the large amt. of isotope fractionation of C and N obsd. in extraterrestrial carbonaceous matter such as in the Murchison meteorite.