The components of asphalt are classified into four classes of compounds:
• saturates, saturated hydrocarbons, the % saturates correlates with softening point of the material
• Naphthene aromatics, consisting of partially hydrogenated polycyclic aromatic compounds.
• Polar aromatics, consisting of high molecular weight phenols and carboxylic acids
• Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds
The naphthene aromatics and polar aromatics are typically the majority components. Additionally, most natural bitumens contain organosulfur compounds, resulting in an overall sulfur content of up to 4%. Nickel and vanadium are found in the < 10 ppm level, as is typical of some petroleum.
The substance is soluble in carbon disulfide. It is commonly modelled as a colloid, with asphaltenes as the dispersed phase and maltenes as the continuous phase. and "it is almost impossible to separate and identify all the different molecules of asphalt, because the number of molecules with different chemical structure is extremely large".
Asphalt/bitumen can sometimes be confused with "coal tar", which is a visually similar black, thermoplastic material produced by the destructive distillation of coal. During the early and mid-20th century when town gas was produced, coal tar was a readily available byproduct and extensively used as the binder for road aggregates. The addition of tar to macadam roads led to the word tarmac, which is now used in common parlance to refer to road-making materials. However, since the 1970s, when natural gas succeeded town gas, asphalt/bitumen has completely overtaken the use of coal tar in these applications. Other examples of this confusion include the asphalt/bitumen of the La Brea Tar Pits and the Canadian oil sands. Pitch is another term sometimes used at times to refer to asphalt/bitumen, as in Pitch Lake.