In studying this topic of oil groups I found that they grouped them mostly by how they were refined, not by their final characteristics such as flash point and carbon chain #'s. But if I was the man in charge decades ago I would of have them grouped by their characteristics instead. For example the bright stock oil that comprises most of Golden Spectro is classified as group 1 but its flash point is higher than synthetics and its carbon chain # is at the low end of group 2 oils so I am adding it to the group 2 oils. Here's a graph showing the viscosities of mineral, castor, and synthetic oils:


Light Oils/Solvents (slightly less carbon chains and boiling points than most group 1 oils)

CAS 64742-88-7 group 1
A complex combination of hydrocarbons obtained from the distillation of crude oil or natural gasoline. It consists predominantly of saturated hydrocarbons having carbon numbers predominantly in the range of C9 through C12 and boiling in the range of approximately 179°C to 210°C
Synonyms: mineral spirits, solvent, turpentine substitute, medium aliphatic solvent naphtha
flash point: 57°C
density: 78 g/mL at 20 °C

64742-48-9 group 1
A complex combination of hydrocarbons obtained by treating a petroleum fraction with hydrogen in the presence of a catalyst. It consists of hydrocarbons having carbon numbers predominantly in the range of C6 through C13 and boiling in the range of approximately 65°C to 230°C (149°F to 446°F).
Synonyms: Hydrotreated heavy petroleum
Viscosity kinematic: 1.23 mm2/s (40°C)
flash point: 62°C
density: 0.775

Group 1 Oils

64742-47-8 group 1
A complex combination of hydrocarbons obtained by treating a petroleum fraction with hydrogen in the presence of a catalyst. It consists of hydrocarbons having carbon numbers predominantly in the range of C9 through C16 and boiling in the range of approximately 150 degree C to 290°C (302°F to 554°F).
Synonyms: Hydrotreated light distillates (petroleum), kerosene
flash point: 71°C
density: 0.776

CAS 68476-30-2 group 1 (source: #1, #2)
A distillate oil having a viscosity of 6.4 cSt @40C, density 0.84 g/cm3, Flash Point: 52°C, Autoignition Temperature: 257°C, Boiling Point: 310°C, with carbon numbers in the range C9 and higher.

CAS 68784-17-8 group 1
Reaction products of fatty acids, C14-C18 (branched and linear) and C18 (unsaturated) with tetraethylenepentamine (linear, branched, cyclic). Isooctadecanoic acid.
Molecular Formula: C18H36O2?C8H23N5
Molecular Weight: 473.785

CAS 64742-46-7 group 1 (source: #1)
A complex combination of hydrocarbons obtained by treating a petroleum fraction with hydrogen in the presence of a catalyst. It consists of hydrocarbons having carbon numbers predominantly in the range of C11 through C25.
Synonyms: Hydrotreated Middle Distillate (Petroleum base oil), white mineral oil, paraffine oil
flash point: 99°C
density: 0.8
boiling point: 254C

CAS 68334-05-4 group 1 (in Red Line AllSport)
Synonyms: Fatty acids, C18-unsatd., dimers, 2-ethylhexyl esters
Molecular formula: C44H80O4
flash point - 38C
Carbon chain - 18

Group 2 Oils
Distillates (petroleum), hydrotreated heavy paraffinic have a flashpoint above 150°C and an initial boiling point of above 280°C.

CAS 64742-01-4 group 2 (Bright Stock)
A complex combination of hydrocarbons obtained as the solvent insoluble fraction from solvent refining of a residuum using a polar organic solvent such as phenol or furfural. It consists of hydrocarbons having carbon numbers predominantly higher than C25 (listed as C26 on one website) and boiling above approximately 400°C (752°F).
Synonyms: Residual oils (petroleum), severely solvent-refined
Flash point: 252ºC (486ºF)
Density: 0.90
Viscosity 454 cSt @ 40ºC

CAS 64741-89-5 group 2 (source: #1)
A complex combination of hydrocarbons obtained as the raffinate from a solvent extraction process. It consists predominantly of saturated hydrocarbons having carbon numbers predominantly in the range of C15 through C30 and produces a finished oil with a viscosity of less than 100 SUS at 100°F (19cSt at 40°C).
Synonyms: Distillates (petroleum), severely solvent-refined light paraffinic oil, white mineral oil, saturated aliphatic hydrocarbons
Density (at 15°C): 0.844
Flash Point [Method]: >190°C [ASTM D-92]
Viscosity: 9.3 cSt (9.3 mm2/sec) at 40°C
boiling point: 280°C
Molecular Formula: C6H13O5P

64741-88-4 group 2 (source: #1)
A complex combination of hydrocarbons obtained as the raffinate from a solvent extraction process. It consists predominantly of saturated hydrocarbons having carbon numbers predominantly in the range of C20 through C50 and produces a finish oil with a viscosity of at least 100 SUS at 100 °F (19cSt at 40 °C).
Synonyms: Solvent-refined heavy paraffinic distillate, mineral oil
flash point: 238°C
density: 0.88 g/cm3 at 25 °C
boiling point 389°C

64742-54-7 group 2
A complex combination of hydrocarbons obtained by treating a petroleum fraction with hydrogen in the presence of a catalyst. It consists of hydrocarbons having carbon numbers predominantly in the range of C20 through C59 and produces a finished oil of at least 100 SUS at 100.degree.F (19cSt at 40°C). It contains a relatively large proportion of saturated hydrocarbons.
Synonyms: Hydrotreated (mild) heavy paraffinic distillate
flash point: 200°C
density: 0.86

CAS 64742-65-0 group 2
A complex combination of hydrocarbons obtained by removal of normal paraffins from a petroleum fraction by solvent crystallization. It consists predominantly of hydrocarbons having carbon numbers predominantly in the range of C20 through C50 and produces a finished oil with a viscosity not less than 100 SUS at 100°F (19cSt at 40°C).
Flash Point: 185 °C
Density: 0.88 g/mL at 25 °C(lit.)
Molecular Formula: Petroleum hydrocarbon (petroleum has a mixture of different oil molecules which is why they don’t specify one here)
Hydrocarbons: C20 - C50
Synonyms: Mineral oil, petroleum distillates, solvent-dewaxed heavy paraffinic

CAS 64742-52-5 group 2
A complex combination of hydrocarbons obtained by treating a petroleum fraction with hydrogen in the presence of a catalyst. It consists of hydrocarbons having carbon numbers predominantly in the range of C20 through C50 and produces a finished oil of at least 100 SUS at 100°F (19cSt at 40°C).
Synonyms: Hydrotreated (mild) heavy naphthenic distillate
flash point: 185°C

CAS 848301-69-6 group 2
Heavy paraffinic base oil obtained using Fischer-Tropsch Synthesisof natural gas.
Carbon #'s C18-C50
flashpoint 183 C

CAS 64742-62-7 group 2 (source: #1)
A complex combination of hydrocarbons obtained by removal of long, branched chain hydrocarbons from a residual oil by solvent crystallization. It consists of hydrocarbons having carbon numbers predominantly greater than C25 and boiling above approximately 400°C (752°F).

CAS 64742-70-7 group 2
A complex combination of hydrocarbons obtained from a catalytic dewaxing process. It consists predominantly of hydrocarbons having carbon numbers predominantly in the range of C20 through C50 and produces a finished oil with a viscosity of at least 100 SUS at 100 degree F (19cSt at 40°C).

Synthetic Oils

CAS 11138-60-6 group 5 (in Super M)
Synonyms: Caprylic acid, TRICAPRYLATE/TRICAPRATE, Trihydroxymethylpropyl ester
Molecular Formula: C60H116O12
Hydrocarbons: C60
Flash Point: 238ºC
Density: 0.953g/cm3