oil refining is the name for a number of processes from chemical engineering, which transform crude oil into useful products such as different fuel oils, liquefied petroleum gas, gasoline, kerosene or diesel oil. these transformation occur in plants called petroleum refineries. the transformations are done in many steps. the refineries are large industrial complexes, that have many different sub-units, and facilities. each refinery has its own unique arrangement and combination of refining processes. the exact setup of the refinery is largely determined by the its location, desired products and economic considerations.