Thermal cracking is a process in which hydrocarbons present in crude oil are subject to high heat and temperature to break the molecular bonds and breaking down long-chained, higher-boiling hydrocarbons into shorter-chained, lower-boiling hydrocarbons. Thermal cracking is often used to upgrade very heavy fractions or to produce light fractions or distillates, burner fuel and/or petroleum coke. Two extremes of the thermal cracking in terms of product range are represented by the high-temperature process called “steam cracking” or pyrolysis (ca. 750 °C to 900 °C or higher) which produces valuable ethylene and other feedstocks for the petrochemical industry, and the milder-temperature delayed coking (ca. 500 °C) which can produce, under the right conditions, valuable needle coke, a highly crystalline petroleum coke used in the production of electrodes for the steel and aluminium industries. More and more, thermal cracking is being replaced by catalytic cracking as this produces end products with a higher octane rating and therefore more economic value.