Benzene. Computer model of a molecule of benzene. Atoms are represented as spheres. The molecule consists of a ring of six carbon atoms, each with an attached hydrogen atom. Benzene is a highly flammable colourless liquid with a characteristic smell. It is obtained commercially from petroleum. Benzene is used as an additive in petrol, to manufacture other chemicals, and as a solvent for many simple organic compounds. Benzene is a carcinogen, with longterm exposure causing leukaemias (cancers of blood cells).