After distillation, fossil fuels can be further refined to produce more of the products that are wanted. For example, larger hydrocarbons can be broken or undergo a “cracking” process to make smaller, lighter hydrocarbons. There are two cracking methods: fluid catalytic cracking and hydrocracking. Fluid Catalytic cracking (FCC) uses high temperatures and a catalyst to break down heavy gas oils into mostly gasoline. Hydrocracking uses catalysts to encourage a reaction between gas oil (a type of fuel oil, somewhat heavier than kerosene) and hydrogen under high pressure and high temperatures to make both jet fuel and gasoline.

In the opposite way, smaller hydrocarbons can be combined through a process called alkylation in order to make larger hydrocarbons, such as those for gasoline.

Heavier products from the distillation of crude oil, called residuum, can also be refined in order to improve its value. They can be cooked at high temperatures in the absence of air within “cokers” to remove moisture, tars, oils and gases. What is left is harder “coke” that is used within furnaces for making steel, and lighter fossil fuels including gasoline, diesel and kerosene.