Cracking of petroleum yields light oils (corresponding to gasoline), middle-range oils used in diesel fuel, residual heavy oils, a solid carbonaceous product known as coke, and such gases as methane, ethane, ethylene, propane, propylene, and butylene. Depending on the end product, the oils can go directly into fuel blending, or they can be routed through further cracking reactions or other refining processes until they have produced oils of the desired weight. The gases can be used in the refinery’s fuel system, but they are also important raw materials for petrochemical plants, where they are made into a large number of end products, ranging from synthetic rubber and plastic to agricultural chemicals.