What is Base Oil? Group I, II, III, IV and V Explained

How base oil is classified

The American Petroleum Institute (API 1509 Annex E) classifies base oils into five groups based on three properties: sulphur content, saturates content, and viscosity index (VI).

Groups I, II and III are refined from crude oil. Group IV is synthetic polyalphaolefin (PAO). Group V is everything else — esters, polyalkylene glycols, naphthenics, silicones.

• Group I — Solvent refined. <90% saturates, >0.03% sulphur, VI 80–120. The original base oil.
• Group II — Hydroprocessed. ≥90% saturates, ≤0.03% sulphur, VI 80–120. The modern workhorse.
• Group III — Severely hydrocracked / hydroisomerised. ≥90% saturates, ≤0.03% sulphur, VI ≥120. Synthetic-grade performance from crude.
• Group IV — PAO synthetic. Built from ethylene gas. Predictable, expensive.
• Group V — Esters, naphthenics, PAGs and all other non-conforming oils. Specialty applications.

What the grade names mean

When a buyer asks for 'SN150' or '500N', they're naming the viscosity. SN = Solvent Neutral (Group I). N alone usually means Group II. The number is the approximate Saybolt Universal Seconds viscosity at 100°F.

Common grades in Asia: SN150, SN500, SN650, Bright Stock (Group I); 150N, 500N, 600N (Group II); 4 cSt and 6 cSt ADbase, YUBASE or Nexbase (Group III).

Which group should you blend with?

Group I is still cheapest and dominates marine engine oils, industrial gear oils and process oils where API SN-level performance isn't required.

Group II is the global standard for passenger car and heavy-duty engine oils. Better oxidation stability, lower volatility, and the regulatory tailwind of low sulphur make it the default unless cost forces Group I.

Group III delivers near-PAO performance — VI ≥120, very low Noack volatility, excellent low-temp pumpability — at a fraction of the price. The mainstream choice for synthetic-blend and full-synthetic motor oils.

Where Southeast Asia sources base oil

South Korea (S-Oil ADbase, SK YUBASE) dominates Group III exports to Asia. Taiwan (Formosa) and the Middle East Gulf (Luberef, Adnoc) supply Group II. Group I still comes from a mix of Indian, Iranian, Russian and aging European plants.

Sanyang Petroleum, a Malaysia-based principal trader under Canven Group, supplies all three groups in flexitank, ISO tank and bulk vessel parcels to Vietnam, Thailand, the Philippines, Indonesia and Malaysia.

Frequently asked questions

What is the difference between Group I and Group II base oil?

Group I is solvent refined with under 90% saturates and over 0.03% sulphur. Group II is hydroprocessed with at least 90% saturates and below 0.03% sulphur. Group II has better oxidation stability and is the modern workhorse for engine oils.

Is Group III base oil considered synthetic?

In most markets, yes. A landmark 1999 ruling in the US allowed Group III base oils to be marketed as 'synthetic' because their molecular structure after hydroisomerisation is functionally equivalent to PAO for most performance metrics — at a much lower cost.

What does SN150 mean?

SN150 means Solvent Neutral 150 — a Group I base oil with a viscosity around 150 SUS at 100°F. It is one of the most widely traded base oil grades globally.

Where can I buy base oil in Southeast Asia?

Sanyang Petroleum trades Group I, II and III paraffinic base oil and naphthenic base oil across Vietnam, Thailand, the Philippines, Indonesia, Malaysia and Singapore in flexitank, ISO tank and bulk vessel parcels.