[TheWiz]

Here is a formula for a liquid preservative system I developed and used in a wide variety of personal care items, including gels, creams and shampoo/Bath formulas for years.  It never failed.

Propylene Glycol  66%
Methyl Paraben  11%
Propyl Paraben  3%
Phenoxyethanol  20%

Procedure: 

Phase A
Heat Propylene Glycol and add with mixing Methyl Paraben and Propy Paraben until Parabens are completely dissolved and mixture is clear.
Phase B
Cool to below 40C and add Phenoxyethanol with mixing.

Finished product will be crystal clear, and extremely effective.

Use percentage, depending on certain types of actives, between 0.5%  - 1.5%.

I hope this helps.