Mansoor,
The sulphur content is largely dependent on the crude oil itelf. The sulphur content in crude from Middle East may differ from crude in Venezuella and so on. Most refineries employ sulphur stripping or desulphurization operations.
Under the new (Group wise)categorisation of Base oils the values of Sulphur permitted are as follows:
1. Group I > 0.03% Sulphur
2. Group II <_ 0.03% Sulphur
3. Group III <_ 0.03% Sulphur
In many cases lubricants are additivated with Sulphur compounds, as in the case of many Metal working and deformation products, in such cases we can observe upto 10% Sulphur. The sulphur in this instance is in a compound form and rarely termed "free suphur." . To enhance performance free suphur is also added to many Metal working or cutting oils.
To answer your question, the base oil Grouping defines the lowest amount of Sulphur % permitted.
Hussam Adeni