What is the base oil?

Time：

2026-02-08

What is the base oil?

In the world of industrial formulation and automotive engineering, the lubricant is often saw as a singular product. However, for the manufacturer, we know that a lubricant is a complex chemical system. At the very heart of this system lies the "foundation"—the base oil.

To understand a lubricant, one must first thing the principle of its primary component - base oil.

Usually, base oil accounts for 70% to 99% of a lubricant's volume. While the base oil and additives work in tandem to provide protection, the base oil serves as the carrier that dictates the fluid's fundamental thermal stability, solvency, and flow characteristics.

What is oil base used for?

The "base oil" is the primary building block for nearly every lubricant used(include grease), Its primary purpose is to provide the liquid volume and the initial hydrodynamic film that separates moving metal parts. Without a high-quality oil base, the additive chemicals in an additive package would have no medium to travel through the engine or machinery.

In manufacturing, the choice of base oil is determined by the end application.

For example, high-speed turbine oils require ultra-stable synthetic bases, while general-purpose industrial hydraulic fluids might utilize cost-effective mineral bases like base oil 150n or base oil 500n. Essentially, the base oil is used to:

Blending with additive packages to produce lubricants such as engine oil, hydraulic oil, etc.
By dissolving additives such as anti-wear agents and extreme pressure additives, grease is produced.
Deeply refined base oil, suitable for food-grade applications
Manufacturing lubricant additives

Detailed Content: Properties of Base Oil

The performance of a lubricant is a direct reflection of the physical and chemical properties of its base oil. When evaluating base oil types, formulators look at the following six critical characteristics:

1. Lubricity (Viscosity and Film Strength)

Lubricity is the most fundamental property. It refers to the oil's ability to reduce friction. This is largely governed by the oil's viscosity—its resistance to flow. A base oil must provide enough "body" to keep metal surfaces apart under load. This is why heavy-duty applications often utilize high-viscosity stocks like base oil 500n, whereas lighter applications might prefer base oil 150n.

2. Cooling (Heat Dissipation)

Internal combustion engines and high-speed gearboxes generate immense heat. The base oil acts as a heat sink. It must have high thermal conductivity and specific heat capacity to absorb thermal energy from the pistons or gears and carry it to the oil cooler or sump. If the base oil degrades under this heat, it loses its ability to cool, leading to mechanical failure.

3. Cleaning (Solvency and Dispersancy)

While additives handle much of the cleaning, the "solvency" of the base oil is critical. Solvency refers to the oil's natural ability to dissolve impurities and keep oxidation byproducts in solution. Group I mineral oils often have higher natural solvency than highly refined Group III oils, which is a key consideration when mixing base oil and additives.

4. Anti-corrosion (Surface Protection)

Base oil serves as a physical barrier between metal and the atmosphere. By coating the surface, it prevents oxygen and moisture from reaching the metal substrate. High-quality base oils have low acidity (low Total Acid Number) to ensure they do not contribute to the very corrosion they are meant to prevent.

5. Sealing (Elastomer Compatibility)

In any closed system, seals and gaskets prevent leaks. The base oil must be compatible with these elastomers. Certain base oil types can cause seals to shrink and become brittle, while others cause them to swell slightly (which can be beneficial for preventing leaks in older machinery).

6. Environmental Properties

Modern base oil manufacturers are increasingly focused on biodegradability and toxicity. Synthetic esters and certain high-grade polyalphaolefins (PAOs) offer better environmental profiles, which is essential for lubricants used in marine environments or "total loss" lubrication systems.

Detailed Content: Classification of Base Oil

To standardize the industry, the American Petroleum Institute (API) created the base oil groups classification system. This system categorizes oils based on their saturates content, sulfur levels, and Viscosity Index (VI).

API Classification System

Group	Sulfur	Viscosity Index	Description
Group I	> 0.03%	80 to 120	Solvent-refined mineral oil. Common for base oil 150n and 500n.
Group II	< 0.03%	80 to 120	Hydrocracked mineral oil. Offers better oxidation resistance.
Group III	< 0.03%	> 120	Severely hydrocracked. Often marketed as "Synthetic."
Group IV	0%	> 140	Polyalphaolefins (PAO). Purely synthetic, high performance.
Group V	-	-	All others (Esters, PAGs, Naphthenics, etc.).

When discussing base oil 150n and base oil 500n, we are typically referring to "Neutral" solvent-refined oils (Group I or II). The number represents the approximate viscosity in SUS (Saybolt Universal Seconds) at 100°F. These are the workhorses of the global industrial lubricant market.

Global Capacity Distribution

The landscape of global base oil manufacturers has shifted dramatically over the last decade. Historically, Group I plants dominated Europe and North America. However, as environmental regulations tighten and engine designs require lower viscosity (e.g., 0W-20 oils), the world has seen a massive move toward Group II and Group III production.

Asia-Pacific: Currently the powerhouse of Group III production, led by manufacturers in South Korea and China.

Middle East: A growing hub for high-purity GTL (Gas-to-Liquid) base oils.

North America: Dominated by Group II production, catering to the massive HDEO (Heavy Duty Diesel Engine Oil) market.

Understanding these base oil types and their availability is crucial for wholesalers who must manage supply chain risks while maintaining consistent product quality.

No.	Company / Refinery	Location	Capacity (barrels/day)	API Group
1	ExxonMobil – Jurong Island	Singapore	~51,900 b/d	Group II
2	ExxonMobil – Baytown	Texas, USA	~32,000 b/d	Group I, II (III expansion)
3	Motiva Enterprises – Port Arthur	Texas, USA	~40,300 b/d	Group II
4	Chevron – Pascagoula	Mississippi, USA	~25,000 b/d	Group II
5	Shell – Pearl GTL	Ras Laffan, Qatar	~28,000 b/d	Group II, III
6	Shell / Hyundai – Daesan JV	South Korea	~25,000 b/d	Group II (III planned)
7	S-Oil (Onsan Complex)	Ulsan, South Korea	~44,700 b/d	Group I, II, III
8	SK Enmove	Ulsan, South Korea	~26,000 b/d	Group III
9	GS Caltex	Yeosu, South Korea	~26,000 b/d	Group II, III
10	Saudi Aramco / Luberef	Yanbu & Jeddah, Saudi Arabia	~12,000 b/d	Group I, II, III
11	Qingyuan Group	Zibo, China	~28,000 b/d	Group II
12	Qinghe Chemical Technology	Zibo, China	~28,300 b/d	Group II

Conclusion

What is the base oil? It is more than just refined petroleum; it is a carefully engineered chemical foundation. Whether you are utilizing a traditional base oil 500n for an industrial gear oil or a cutting-edge Group IV PAO for a high-performance engine lubricant, the base oil dictates the limits of your product's performance.

FAQ

1. Is base oil the same as lube oil?

Not exactly. Base oil is the raw, unblended additive components. Lube oil (or lubricant) is the final product created by mixing the base oil and lubricant additives. Base oil is the ingredient; lube oil is the recipe.

2. What is another name for base oil?

Base oil is often referred to as base stock, neutral oil (if it is Group I or II), or carrier oil in the context of chemical blending.

References

Wikipedia - Base oil

Industry Resource (Machinery Lubrication)

None

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