Preservatives, General Rules, from Lab Rat
If your formula contains water, you can use:
Germaben II
Germaben II-E
Germall Plus
Liquid Germall Plus
Uniphen P-23
Phenonip
LiquaPar PE
LiquaPar Optima
If your formula contains only oils, butters and waxes and does not contain water, you don't need a preservative.
If your formula contains only oils, butters and waxes and does not contain water but there is a possibility that the consumer could introduce water into the product, you can use:
Uniphen P-23
Phenonip
LiquaPar PE
LiquaPar Optima
LiquaPar Oil
There are other factors that come into play, so this is just a "general rule of thumb" for starters. Hopefully others will chime in?