I have heard the terminology of group 1, group 2, group 3 etc applied to lube oil.
Can anyone explain what that means?

EPete
I have heard those groups used with Grease but not oil.

Group 1,2,3,4,& 5 oils refer to the base oil that is in a particular lubricant or grease product. The grouping refers to the processing that has been done to the oil. I don't remember the exact specs, but it deals with sulfur content and % removal of aromatics and the viscosity index of the oil. The higher the group number, the more refined the base stock is. Group 4 as well as 5 is a pure synthetic and anything below that is truly not a synthetic oil, but Group 3 Base oils are allowed to be called synthetic at this point. The better the base oil, the higher your viscosity index is and the less amount of additives are needed to achieve the results needed. There are also alot of lubricants that are made through blending different groups of the base oils to achieve results.

The was a very extensive post regarding oil groups and the differences on the BoBs the Oil Guy website. http://www.bobistheoilguy.com/ I think its still there.

Thanks everyone. I did find on that website a link to a pdf

http://www.prod.exxonmobil.com/refiningtechnologies/pdf/base_oil_refining_lubes_daage_france070601.pdf

On page 4 of that pdf I found the follownig table:
API Group | Sats| Sulfur| VI |Typical Manufacturing Process
I |<90% |>0.03%| 80-119| Solvent Processing
II| >90%| <0.03%| 80-119| Hydroprocessing
III| >90%| <0.03%| 120+| Wax Isomerization, H/C, GTL
IV| n.a.| n.a| Polyalphaolefins (PAO)
V| All Other Basestocks

This seems to match the parameters Bradley mentioned.