High-density polyethylene. Used in the manufacture of plastic items such as plastic pipe, grocery bags, water coolers and milk bottles.

Heavy Bottoms

Thick, black substances that remain in refinery stills after all lighter fractions have been processed out of the feedstock.

Heavy Crude

Crude oil of 20-degree API gravity or less; often very thick and viscous.


A petroleum liquid found in small amounts in condensates; one of the components of natural gasoline.


A key feedstock in the manufacture of many high-density and linear low-density polyethylene resins, which are used to make food and drink containers, trash bags, plastic pipe and other consumer products.

Horizontal Drilling

The technique for cutting a hole in geological strata in a horizontal, rather than the normal vertical, direction.


Organic chemical compounds of hydrogen and carbon atoms that form the basis of all petroleum products. They may exist as solids, liquids or gases.


Catalytic cracking of hydrocarbon feedstocks in the presence of hydrogen.


The process of converting any type of organic sulphur compound into hydrogen sulphide and hydrocarbons in order to reduce the sulphur content of petroleum products complying with the required fuel specifications (includes gas oil and kerosene desulphurisation).

Hydroskimming refinery

A refinery with a configuration which only includes distillation, reforming, some hydrotreating, and occasionally sulphur recovery processes.


The process whereby feedstocks are place into contact with hydrogen, under high pressure and at a high temperature, in the presence of a catalyst, to reduce the content of sulphur, nitrogen, metals, polyaromatics and olefins.