Crude oil

Crude oil is not a compound and has no formula. It is a mixture of thousands of hydrocarbons, varying enough between fields that grades are traded as separate commodities, and a refinery is built for the crude it expects to receive.

Most of a barrel becomes fuel. The part that matters here is the light fraction — naphtha — which is the feedstock for almost every synthetic polymer in use. Roughly a twentieth of world oil production ends up as plastic, which is small next to combustion and large next to everything else made from it.

Fractional distillation separates the mixture by boiling point: gases at the top of the column, then naphtha, kerosene, diesel, and residue at the bottom. Nothing is chemically changed at this stage — the fractions were already there.

The chemistry comes afterwards. Cracking breaks long molecules into short ones, reforming rearranges them, and it is cracking that produces the small reactive molecules polymers are built from. A refinery configured for fuel and one configured for petrochemicals make very different cuts from the same barrel.

As fuel, in a volume nothing else approaches. As the feedstock for polymers, solvents, detergents, synthetic fibres, fertiliser precursors, lubricants and bitumen. As asphalt, which is the bottom of the barrel used as a road.

The materials argument and the energy argument pull apart here and are constantly conflated. Ending combustion does not end petrochemical demand, and a polymer industry supplied from a fifth of current production would still need the molecules from somewhere.

Used from natural seeps for millennia — as bitumen for waterproofing and mortar in Mesopotamia long before anyone drilled for it. The industry begins in the 1850s and 1860s with kerosene for lamps, which was the product that mattered; petrol was initially a waste stream with no market.

The petrochemical use is a twentieth-century afterthought that became the second reason the industry exists. Almost every polymer in common use postdates 1930, and none of them would have been economic without a cracking industry already built for fuel.

The combustion argument is not a materials question and is not made here. What is a materials question: a polymer made from oil locks its carbon into a solid rather than releasing it, and releases it at end of life only if the object is burned.

The extraction impacts are local and real — produced water, flaring, spills, and the disturbance of drilling — and they attach to the barrel rather than to any one product made from it. Attributing them to plastic specifically requires deciding how to allocate a shared feedstock, and every method of doing so gives a different answer.