Any of a variety of analytical techniques carried out to determine the composition of a crude oil by breaking it down into basic chemical components. The hydrocarbon components are usually identified by carbon number fractions: C₁, C₂, C₃, etc. Up to C_n, where the limiting carbon number, n, is defined by the particular analytical technique. These analytical techniques include, but are not limited to, gas or liquid chromatography, cryogenic and flash distillations, true boiling-point distillations, structural fluid characterizations such as polynuclear aromatic hydrocarbon analysis, SARA analysis, sonic testing and other crude oil assay methods. Other nonhydrocarbon components can also be identified, such as nitrogen, heavy metals, sulfur and salts.