Well , did some reading:
you are expected to use only vacuum pump oil for vacuum pumps (imagine that). Unless you are a chemist don't put anything else in there if you care for the life of the tool and the final vacuum level.
Vacuum pump oil is graded for different types of pumps, different speeds and different vacumm levels, so it is tricky business, your manufacturer will supply those.
Also if you're in doubt about the oil you have - if it is yellowish or any other colour - don't use it. The good vacuum pump oil must bea clear/transparent.
Also Shell makes something that appears to be general use vacuum pump oil - SHell Corena V