Next step after desalting is atmospheric distillation. NoDoC cost model considers the crude distillation unit that separates the crude oil into its naturally occurring components. This is known as separation. A furnace heats and partly vaporizes the "feed stream". The vapor and liquid mixture is then fed into the bottom section of the atmospheric distillation tower. As the vapor rises, it cools down and the different components condensate. Products from the distillation tower range from gases at the top to very heavy, viscous liquids at the bottom. It produces naphtha and other intermediate products, but not gasoline. These product streams are still considered “unfinished” and require further processing to become useful products.