Main-Product

Diesel/gas oil is a middle distillate hydrocarbon fraction boiling in the approximate range of 180–360 °C, composed primarily of C₁₀–C₂₂ hydrocarbons with a carbon number distribution peaking around C₁₄–C₁₆. 

Gas Oil / Diesel Composition

It contains four structural hydrocarbon classes whose relative proportions vary significantly by crude origin and production route:

• Normal paraffins (n-alkanes): Highest cetane quality, but prone to wax crystallisation at low temperatures, limiting cold-flow performance in paraffinic straight-run streams.

• Isoparaffins (isoalkanes): Good cetane quality combined with better cold-flow behaviour than n-paraffins due to branching; predominant in hydrocracked diesel, which accounts for its superior pour point and CFPP.

• Naphthenes (cycloalkanes): Moderate cetane numbers, good cold-flow properties, and significant contributors to density and volumetric energy content.

• Aromatics: Lowest cetane numbers and highest carbon-to-hydrogen ratio, increasing soot emissions on combustion. EN 590 limits polycyclic aromatics to ≤ 8% by mass. A minimum level is nonetheless needed to meet the density floor (≥ 820 kg/m³) and maintain adequate lubricity.

A typical straight-run gas oil contains 20–30% paraffins, 30–40% naphthenes, and 25–40% aromatics, with sulphur ranging from a few hundred to several thousand ppm depending on crude origin. Finished road diesel (EN 590) after hydrotreating carries ≤ 10 ppm sulphur, a minimum cetane number of 51, and a CFPP suited to its climatic class. Hydrocracked diesel is isoparaffin- and naphthene-rich, with aromatics often below 10% and cetane numbers frequently exceeding 55–60.

Gasoil Production

Gasoil is produced from a wide range of feedstocks and refinery process routes, and encompasses several distinct product forms along the refinery-to-market chain — from unprocessed straight-run fractions to refined commercial fuels:

• Straight-run gas oil (SRGO): The unprocessed atmospheric distillation cut drawn directly from crude oil, used as feedstock for further upgrading or as a blendstock for industrial fuel grades.

• Hydrotreated diesel: Straight-run or cracked gas oil upgraded by catalytic hydrotreating to remove sulphur, nitrogen, and unstable olefins; the standard production route for on-road diesel meeting EN 590 (Europe) or ASTM D975 (US) specification.

• Hydrocracked diesel: Diesel-range product recovered from a hydrocracker processing heavier atmospheric or vacuum gas oil feedstocks; characterised by high paraffin content, very low sulphur, and excellent cetane quality.

• FCC Light Cycle Oil (LCO): A cracked, highly aromatic diesel-range stream from a fluidised catalytic cracker, typically used as a blendstock after hydrotreatment due to its low cetane number and high aromatic content.

• Coker gas oil: Diesel-range distillate from a delayed or fluid coker, requiring hydrotreating before use as a finished fuel blendstock.

Commercial Grades

The diesel product family spans a broad range of commercial grades — including automotive diesel (ADO), high-speed diesel (HSD), heating oil, marine diesel oil (MDO), off-road / red diesel, light diesel oil (LDO), and straight-run gas oil (SRGO) as a refinery intermediate — differentiated by sulphur content, ignition quality, cold-flow specification, and applicable duty regime rather than by fundamentally different molecular character. All grades share the same core distillation range and hydrocarbon chemistry; specification differences reflect end-use performance requirements and the regulatory frameworks of the markets they serve.