By Sinopec Online Technical Team
Introduction
This reference guide summarises the key specifications and typical physical properties of base oils by API group classification. Understanding viscosity, volatility, sulphur content, and saturation levels is essential for selecting base stocks for engine oils, industrial lubricants, and greases. Sinopec Online provides this reference to support formulators, buyers, and engineers in technical decision-making.
API Base Oil Group Definitions
| Group | Saturates (%) | Sulphur (wt %) | Viscosity Index | Production Method |
|---|---|---|---|---|
| Group I | < 90 | > 0.03 | 80–120 | Solvent refining and dewaxing |
| Group II | ≥ 90 | ≤ 0.03 | 80–120 | Hydrocracking and hydrotreating |
| Group III | ≥ 90 | ≤ 0.03 | > 120 | Severe hydroisomerisation and hydrocracking |
| Group IV | n/a | n/a | ≥ 125 | Polyalphaolefins (synthetic) |
| Group V | n/a | n/a | Varies | Esters, PAGs, and other synthetics not in Groups I–IV |
Typical Physical Property Ranges
| Property | Group I | Group II | Group III | Group IV (PAO) |
|---|---|---|---|---|
| Kinematic Viscosity @100°C (cSt) | 3 – 35 | 3 – 35 | 3 – 10 | 2 – 12 |
| Viscosity Index | 90 – 105 | 100 – 115 | 120 – 140 | 130 – 150 |
| Pour Point (°C) | -9 to -15 | -12 to -18 | -18 to -30 | -50 to -60 |
| Oxidation Stability | Moderate | Good | Excellent | Excellent |
| Solvency | High | Moderate | Low | Low |
Application Summary
- Group I — Suited to industrial lubricants, greases, and process oils requiring solvency.
- Group II — Common in automotive and industrial oils balancing oxidation stability with cost.
- Group III — Used in high-performance engine oils and low-temperature blends.
- Group IV (PAO) — Synthetic base stocks for severe duty and extended drain intervals.
- Group V — Niche synthetics used for ester and PAG-based formulations.
Industry References
- API Base Oil Group Classification
- ASTM D6074 – Standard Guide for Characterising Hydrocarbon Base Oils
- US Energy Information Administration (EIA)
Cross-References on Sinopec Online
Relevant Product Collections
Published by Sinopec Online Technical Team
