This paper discusses three different systems for olefin production by cracking the following feedstocks - (1) ethane only; (2) ethane acid propane, which are normally simultaneous feedstocks; and (3) liquid hydrocarbons ranging from light naphtha to atmospheric gas oil. The reasons (economically and others) are given why the last feedstock should be regarded as the material of the future. However, the process itself is not so efficient as the production of olefins from ethane and propane.