The separation of olefins from paraffins is energy intensive, and consequently polymer membrane based separations have been considered as an attractive alternative. Although much research has been conducted on polymer membranes for the C3H6/C3H8 separation in recent years, no comprehensive review exists that considers and evaluates all of the available literature data. A review is necessary in order to define the challenges that must be overcome to achieve adequate separation performance using polymer membranes. The goal of this paper is to present the experimentally observed C3H6/C3H8 upper bound based on available literature data, as well as C3H6/C3H8 permeation measurements reported herein. A mathematical prediction of the C3H6/C3H8 upper bound curve was also developed, and it compares very well to the most credible experimentally observed C3H6/C3H8 upper bound.