Crude oil has remained the leading source of fuel or energy in the world. It is a flammable and toxic liquid that contains a complex mixture of hydrocarbons having different molecular weights and other liquid organics. There are varieties of crude oil each with an inimitable mix of molecules that gives its physical and chemical properties and market value. The market value of the crude oil is influenced by the geographical location of its production, the sulfur content and its specific gravity according to the American Petroleum Institute’s (API) system. The crude oil can be separated into several hydrocarbons of useful commercial products by using a process called ‘refining’, which is carried in an oil refinery. The refinery process produced three groups of products: light fraction (e.g. gas such as liquid petroleum gas—LPG, gasoline, aviation fuel, etc.); middle distillates or medium fraction (e.g. kerosene, lubrication oil, light gas oil, diesel oil, etc.); and heavy fraction or bottom residue (e.g. asphalt and bitumen, waxes, etc.). The intermediate distillates can be altered using catalytic reforming to produce new compounds. The refinery plants generate a lot of waste which must be treated to meet the requirement of environmental agencies. In this chapter, the methods and technologies employed in the refinery of crude oil into its various product fractions as well as the types of waste generated at crude oil refineries and their methods of treatment are discussed. An overview of the downstream oil industry in Ghana is also presented.