When most people think of petroleum they think of gasoline and diesel fuel. They may even conjure up images of jet fuel, but most will rarely consider the other unexpected places that petroleum by-products show up in modern life. Because crude oil contains a vast number of different hydrocarbons, various refined products have found their way into everything from plastics to pharmaceuticals.

The industry that uses petroleum to produce other chemicals is referred to as the petrochemical industry. It is estimated that industrialized nations currently consume petrochemical products at a rate of three and a half gallons (approx. 13 litres) of oil per day. That means that, excluding fuel oil, modern life results in each citizen of an industrial nation using over 1,200 gallons (4532 litres) of oil per year.

One of the most important uses of petroleum is in the production of ammonia to be used as the nitrogen source in agricultural fertilizers. In the early 20th century, Fritz Haber invented a process that allowed for industrial scale production of ammonia. Prior to that, ammonia for fertilizer came only from manure and other biological processes.

The Haber process works in two steps. First, methane from natural gas is cleaned to remove sulphur and hydrogen sulphide. It is then reacted with steam over a catalyst to produce hydrogen and carbon dioxide. In the next step, which is the actual Haber process, hydrogen and gaseous nitrogen are reacted at high heat and pressure to produce ammonia, which is siphoned off and added to chemical fertilizers.

Agriculture also depends on the use of pesticides to ensure consistent, healthy crop yields. Pesticides are almost all produced from crude oil.

In essence, from running farm machinery to fertilizing plants, agriculture is one of the largest users of petroleum based products.