The term “base oil” refers to lubrication-grade oils that are initially created by refining crude oil (mineral base oil) or chemical synthesis (synthetic base oil). According to standard definitions, base oil is a type of oil having a boiling point between 550 and 1050 F and a composition of hydrocarbons with 18 to 40 carbon atoms. Depending on the molecules’ chemistry, this oil may be paraffinic or napthenic in composition.

Almost all of the lubricants used in plants today began as simple basic oils. Base oils are divided into five categories by the American Petroleum Institute (API) (API 1509, Appendix E). Out of petroleum crude oil, the first three types are refined. Group IV base oils are polyalphaolefin (fully synthetic) oils. All additional basic oils that are not a part of Groups I through IV fall under Group V. Lubricating oils are initially classified as one or more of these five API categories before any additives are added to the combination.

Group I

Base oils are defined as having a viscosity index ranging from 80 to 120, less than 90 percent saturates, and more than 0.03 percent sulphur. These oils can be used in environments ranging from 32 to 150 degrees Fahrenheit. Base oils from Group I are refined using a solvent, which is a less complex refining method. They are the least expensive base oils available because of this.

Group II

Base oils are described as having a viscosity index between 80 and 120, more than 90 percent saturates, and less than 0.03 percent sulphur. They are frequently produced by hydrocracking, a trickier method than the one used for Group I base oils. These oils have better antioxidation capabilities than Group I base oils because all of their hydrocarbon molecules are saturated. In compared to Group I base oils, they also have a clearer colour and are more expensive. Group II base oils are nevertheless becoming more and more prevalent on the market and are priced quite similarly to Group I oils.

Group III

Base oils have a viscosity index above 120, more than 90% saturates, and less than 0.03 percent sulphur. These oils are typically substantially hydrocracked (greater pressure and heat) and refined even more than Group II base oils. Purer base oil is the goal of this extended process. Group III base oils are sometimes referred to as synthetic hydrocarbons even though they are made from crude oil. These oils are likewise becoming more and more common, just as Group II base oils.

Group IV

PAOs, or polyalphaolefins, are group IV basic oils. Synthesising is the method used to create these synthetic base oils. They are ideal for usage in extremely cold and hot environments because of their substantially wider temperature range.

Group V

All other base oils, such as silicone, phosphate ester, polyalkylene glycol (PAG), polyolester, biolubes, etc., are categorised as Group V base oils. To improve the qualities of the oil, these base oils are occasionally combined with additional base stocks. An illustration would be a polyolester- and PAO-based compressor oil. Esters are typical Group V base oils that are utilised in a variety of lubricant formulations to enhance the base oil’s existing qualities. When compared to a PAO synthetic base oil, ester oils offer superior detergency and can withstand more usage at higher temperatures, extending their useful life.

Typical Properties of Each Base Oil Group

GroupⅠ GroupⅡ GroupⅢ Ultra-S 4,6,8 GroupⅣ
Saturates, % 65~85 93~99+ 95~99+ 99+ 99+
Aromatics, % 15~35 <1~7 <1~5 <1 <1
Sulfur, ppm 300~3000 5~300 0~30 <1 n/a
Viscosity @ 100℃, cSt 4~32 4~30 4~8 4.0~7.6 4~70
Viscosity Index(VI) 95~105 95~118 123~150 120~135 125~150
Pour point, ℃ -15 -15 -15 -22.5 ~ -15 -45

Base stocks are classified inot various grades including Neutral, Solvent Neutral, Bright Stocks, The most common names are for group I (SN: Solvent Neutral), for group II (N: Neutrals) and group III grade names refer to the viscosity (4cst, 6cst, 8cst …).

Group I - Baseoil Grades - Technical Specifications

Characteristic
Units
SN-150
SN-500
Bright Stock
Test Method
Kinematic viscosity at 100°C
cSt
4.4 – 5.6
9.7 – 12.0
min. 28
ASTM  D-445
Kinematic viscosity at 40°C
cSt
28 – 32
90 – 105
ASTM D-445
Viscosity index (VI)
95 – 100
95 – 100
min. 95
ASTM D-2270
Flash Point
°C
min. 195
min. 210
min. 276
ASTM D-92
Sulphur Content
%Wt
0.15 – 0.60
0.15 – 0.60
0.15 – 0.60
ASTM D-2622
Pour Point
°C
max. -6
max. -6
max. -9
ASTM D-97
Density @ 15°C
Kg/L
0.870 – 0.890
0.885 – 0.895
0.900 – 0.910
ASTM D-1298
Color
max. 2
max. 2
max. 2
ASTM D-1500
TAN
mg KOH/g
max. 0.05
max. 0.05
max. 0.05
ASTM D-664
Carbon Residue Content
%Wt
0.04
0.12
0.21
ASTM D-189

Group II - Baseoil Grades - Technical Specifications

Characteristic
Units
N-150
N-500
Test Method
Kinematic viscosity at 100°C
cSt
5.0-5.6
10.0-12.0
ASTM  D-445
Kinematic viscosity at 40°C
cSt
28-32
95-107
ASTM D-445
Viscosity index (VI)
95-110
95-110
ASTM D-2270
Flash Point
°C
min. 210
min. 230
ASTM D-92
Sulphur Content
%Wt
max. 0.012
max. 0.012
ASTM D-2622
Pour Point
°C
max. -12
max. -12
ASTM D-97

Group III - Baseoil Grades - Technical Specifications

Characteristic
Units
4cSt
6cSt
8cSt
Test Method
Kinematic viscosity at 100°C
cSt
4.1 – 4.4
5.7 – 6.5
7.6 – 8.2
ASTM  D-445
Kinematic viscosity at 40°C
cSt
19.0 – 20.0
32.0 – 37.0
43.8 – 50.1
ASTM D-445
Viscosity index (VI)
min. 120
min. 120
min. 120
ASTM D-2270
Flash Point
°C
min. 220
min. 220
min. 220
ASTM D-92
Sulphur Content
%Wt
0.001
0.001
0.001
ASTM D-2622
Pour Point
°C
max. -12
max. -12
max. -12
ASTM D-97
API BASE OIL CATEGORIES
Base Oil Category Sulfur (%) Saturates (%) Viscosity Index
Group I (solvent refined) >0.03 and/or <90 80 to 120
Group II (hydrotreated) <0.03 and >90 80 to 120
Group III (hydrocracked) <0.03 and >90 >120
Group IV PAO Synthetic Lubricants
Group V All other base oils not included in Groups I, II, III or IV