In large scale refinery operations, there are several tiers of products produced. Gasoline and diesel are the desired end products of petroleum refining, however, the petroleum refining process produces many intermediary byproducts that require further refining to produce useful consumer or commercial grade products. Petroleum byproducts are either further refined onsite or transferred to transportation vehicles to a different chemical refining plant. End products – gasoline and diesel – are transferred to offsite loading bays for land, rail, or sea transport.
