By Sinopec Online Technical Team
Introduction
Group II and Group III base oils are the backbone of many modern lubricant formulations. Both come from hydroprocessing, yet deeper conversion and isomerisation in Group III change the molecular distribution and deliver higher viscosity index along with very low sulphur.
Processing overview
Group II
- Hydrocracked and hydrotreated paraffinic stocks.
- High saturates and very low sulphur by API definition.
- Dewaxing may be catalytic or solvent based depending on unit design.
Group III
- Hydrocracked, hydrotreated, and hydroisomerised to shift straight paraffins to iso-paraffins.
- Very high saturates and near zero sulphur, with naturally higher viscosity index.
- Catalytic dewaxing and isomerisation improve low temperature behaviour.
Typical property ranges
The values below are indicative ranges used for selection and do not represent a single supplier’s data.
| Property | Group II | Group III |
|---|---|---|
| Viscosity index | About 95 to 115 | About 120 and above |
| Noack volatility | Lower than Group I | Lower than Group II for like viscosity grade |
| Oxidation stability | High | Very high |
| Sulphur | Very low | Near zero |
| Saturates | High | Very high |
| Solvency | Moderate | Lower than Group II |
| Cold flow | Good | Very good for same kinematic viscosity |
Test methods that matter
- Viscosity index: ASTM D2270
- Volatility: Noack ASTM D5800
- Oxidation stability: ASTM D943 and bench tests used by additive companies
- Cold crank behaviour: CCS ASTM D5293 and MRV ASTM D4684 for finished oils
- Pour point: ASTM D97 or ASTM D5949
- Saturates and sulphur: Group classification tests used to confirm API group status
Formulation trade-offs
- Volatility and fuel economy: Group III helps meet low volatility and high VI targets in modern engine oils.
- Solvency and seal behaviour: Lower solvency in Group III may need additive system adjustment or limited use of higher solvency components.
- Shear stability: Higher VI can reduce dependence on VI improvers, which supports shear stability in severe duty.
- Cost versus performance: Blends of Group II and Group III are common to hit specifications at controlled cost.
Applications
- Passenger car and heavy duty engine oils: Group III supports low volatility and extended oxidation life.
- Industrial lubricants: Group II is widely used in hydraulic, turbine, compressor and circulation oils where balanced solvency and oxidation control are required.
- Low temperature service: Group III improves cold flow for winter grades.
Selection framework
- Start with performance standards that must be met, such as API, ACEA or OEM specifications.
- Choose the base stock that achieves volatility and oxidation targets with the simplest additive treat.
- Check low temperature limits and pumpability margins for your climate and duty.
- Validate material compatibility and seal performance.
- Optimise cost by blending Group II and Group III where appropriate.
Cross-References
- Base Oil Market Report – October 2025
- Group I vs Group II Base Oils: Key Differences and Applications
- Brightstock and Heavy Neutral Oils: Role in Modern Lubricant Blends
Relevant base oil categories
- Engine Oil collection
- Hydraulic Oil collection
- Industrial Lubricants collection
- Gear Oil collection
- All Products
Published by Sinopec Online Technical Team
