Professional buyer’s guide
Base Oil Groups Explained: How to Choose Between Group I, II, III and IV
Compare the principal base oil groups, understand Özerşah Group’s available grades and prepare a technically complete quotation request.
Choosing a base oil is not simply a matter of selecting the highest group number. Lubricant manufacturers must balance viscosity, formulation compatibility, operating conditions, target specifications and cost. Procurement teams must also consider quantity, packaging, destination and delivery requirements.
Group I, II, III and IV describe broad base-stock classifications, while labels such as SN 150, 150N, 4 cSt and PAO 4 identify different grades or viscosity positions. Similar numbers do not necessarily mean equivalent products.
This guide explains the principal differences between the base oil groups, outlines the grades available through Özerşah Group and provides a practical framework for preparing a technically complete quotation request.
What Are Base Oils?
Base oils are the principal fluid components used to formulate lubricants and greases. A finished lubricant normally contains one or more base stocks combined with an additive system selected for the intended application and performance target.
The terms “base oil” and “base stock” are often used interchangeably. More precisely, a base stock is an individual lubricant component from a particular producer, while a base oil may consist of one or more base stocks within a finished formulation.
Viscosity may be expressed in centistokes (cSt), a unit of kinematic viscosity. Buyers should confirm the test temperature, method and specification values in the applicable technical documentation rather than relying on the grade name alone.
Understanding the Different Base Oil Groups
The API classification system distinguishes Groups I–III using saturates, sulfur content and viscosity index.
Saturates are stable hydrocarbon molecules. Sulfur is one of the components reduced during refining. Viscosity index indicates how much an oil’s viscosity changes as temperature changes; a higher value generally means less variation across the measured temperature range.
Group IV is different because it is defined by its chemistry: polyalphaolefin, commonly shortened to PAO.
These classifications provide a useful starting point, but they do not guarantee identical performance among products in the same group. Individual base stocks can differ in viscosity, volatility, low-temperature behavior and other properties.
Finished-lubricant performance also depends on the complete formulation. Product specifications, formulation compatibility and appropriate testing must therefore be reviewed before selection.
Group I Base Oils
Group I base oils are generally produced using solvent-assisted separation processes. Their characteristics can provide useful solvency, while the group also includes heavier components for formulations requiring higher viscosity.
- SN 150
- SN 500
- Bright Stock SN 350
SN 150 and SN 500 occupy different viscosity positions. Bright stock is a high-viscosity component generally considered when additional viscosity or solvency is required.
Group II Base Oils
Group II base oils are generally produced through hydrogen-based refining processes. They typically provide greater oxidation stability and purity than conventional Group I stocks.
- 70N
- 100N
- 150N
A product identified as 150N should not be assumed to be interchangeable with SN 150. Similar numbers do not establish identical chemistry, viscosity or additive response.
Group III Base Oils
Group III base oils are generally produced through more severe hydrogen-based processing. They have a viscosity index of at least 120 and may be considered where stronger temperature-viscosity behavior is required.
- 4 cSt
- 6 cSt
These labels identify viscosity classes. Buyers should verify the complete specification, typical values and relevant test methods before selection.
Group IV PAO Base Oils
PAOs are synthetic hydrocarbon base stocks. They are often evaluated for formulations requiring strong oxidation stability, low-temperature fluidity or performance across a broad temperature range.
- PAO 4
- PAO 6
- PAO 8
PAO is not automatically the best choice for every lubricant. Cost, additive response, target viscosity and the complete formulation must be considered.
Base Oil Groups I–IV Comparison Table
This table provides general group-level guidance. It does not replace a technical data sheet, product specification or formulation evaluation.
| Group | Production or chemistry | API classification basis | Typical considerations | Özerşah Group grades |
|---|---|---|---|---|
| Group I | Primarily solvent-refined mineral base stock | Viscosity index from 80 to below 120; falls outside one or both Group II limits for saturates and sulfur | Established formulations, solvency and heavier viscosity options | SN 150, SN 500, Bright Stock SN 350 |
| Group II | Hydroprocessed mineral base stock | At least 90% saturates, no more than 0.03% sulfur and viscosity index from 80 to below 120 | Typically greater oxidation stability and purity than Group I | 70N, 100N, 150N |
| Group III | More severely hydroprocessed base stock | At least 90% saturates, no more than 0.03% sulfur and viscosity index of at least 120 | Higher viscosity index and typically stronger temperature-viscosity performance | 4 cSt, 6 cSt |
| Group IV | Synthetic polyalphaolefin | Defined as PAO rather than by the numerical limits used for Groups I–III | Typically strong low-temperature and oxidation performance; formulation and cost require evaluation | PAO 4, PAO 6, PAO 8 |
These are broad distinctions. Actual properties must be confirmed for the individual grade and supply under consideration.
How Buyers Should Select a Base Oil
A technically sound selection process starts with the finished product rather than the supplier’s list of available grades.
Define the finished-lubricant requirement
Identify the intended application, target viscosity grade, required industry, OEM or customer specification, operating conditions, intended service interval and destination-market requirements.
Businesses developing new products or complete ranges can also explore Özerşah Group’s private label lubricant manufacturing services.
Establish the required viscosity range
- Target finished-lubricant viscosity
- Required base-stock viscosity
- Whether multiple base stocks will be blended
- Need for a heavier component
- Low-temperature viscosity requirements
Evaluate the operating environment
Important factors include minimum and maximum temperatures, oxidation exposure, equipment load, volatility sensitivity, expected operating duration and equipment compatibility.
These considerations help define the required performance level, but they should not be converted into an automatic grade recommendation.
Review the additive system
Base oils and additives work as a complete system. A formulation developed with one base stock may respond differently when the group, grade, supplier or manufacturing source changes.
A change may require:
- Technical review
- Laboratory blending
- Compatibility checks
- Performance testing
- Reformulation or renewed validation
Özerşah Group’s lubricants industry consultancy can support discussions involving product selection, lubricant knowledge and portfolio development.
Compare technical and commercial information
- Technical requirement Confirm viscosity, performance targets and formulation constraints.
- Documentation Define the product and shipment documents required for review.
- Logistics Specify packaging, destination and receiving capabilities.
- Commercial alignment Confirm quantity, requested delivery window and availability.
Buyers interested specifically in IBC and ISOTANK arrangements can review Özerşah Group’s guide to bulk Group I and Group II base oil supply .
Özerşah Group’s Available Base-Oil Portfolio
As a base oil supplier in Turkey serving professional buyers, Özerşah Group can discuss requirements across the following portfolio:
| Base oil group | Grades |
|---|---|
| Group I | SN 150, SN 500, Bright Stock SN 350 |
| Group II | 70N, 100N, 150N |
| Group III | 4 cSt, 6 cSt |
| Group IV | PAO 4, PAO 6, PAO 8 |
This portfolio summary does not indicate that every product is currently in stock. Grades, quantities, packaging options and delivery feasibility must be confirmed for each inquiry.
Buyer Inquiry Checklist
A complete inquiry helps the base oil supplier assess both the technical and logistical requirements.
- Required grade Include the group and full grade name.
- Required quantity State the quantity and unit clearly.
- Packaging Specify the preferred receiving format.
- Destination Include the city, port and country.
- Target date Provide the required delivery window.
It is also helpful to include the intended application, target finished-product specification, critical technical requirements, required documents and any destination-specific handling instructions.
Providing complete information supports a more accurate assessment. It does not constitute confirmation of product availability, price or delivery timing.
Frequently Asked Questions About Base Oil Groups
What is the difference between a base oil group and a base oil grade?
The group describes broad refining or chemical characteristics. The grade identifies a viscosity class or position within a product range. Both must be considered during selection.
Is a higher base oil group always better?
No. The appropriate group depends on the formulation, application, performance requirements, additive system and commercial objectives.
Are Group III and Group IV base oils the same?
No. Group III base oils are classified using defined limits for saturates, sulfur and viscosity index. Group IV consists of synthetic PAO base stocks.
Are SN 150 and 150N interchangeable?
Not automatically. Similar numbers do not demonstrate equal viscosity properties, chemistry, additive response or finished-lubricant performance.
Can one base oil be replaced by another from the same group?
Not without evaluation. Products within the same group can have different properties. Testing or renewed validation may be necessary.
Which base oil grades are available through Özerşah Group?
The portfolio includes Group I SN 150, SN 500 and Bright Stock SN 350; Group II 70N, 100N and 150N; Group III 4 cSt and 6 cSt; and Group IV PAO 4, PAO 6 and PAO 8. All grades and availability are subject to confirmation.
What information is needed for a quotation?
Provide the required grade, quantity, preferred packaging, delivery destination and target delivery date. Application and technical details can help Özerşah Group evaluate the inquiry more effectively.
Confirm the Right Grade and Request a Quotation
Base oil groups provide a useful classification framework, but they are only the beginning of the purchasing decision. Send Özerşah Group your:
- Required grade
- Required quantity
- Preferred packaging
- Delivery destination
- Target delivery date