Preparative HPLC and HPLC-MS are well established as the methods of choice for purification of pharmaceutical library compounds. Recent advances in supercritical fluid chromatography (SFC) have now made SFC a viable alternative to HPLC for this application. One of the potential arguments for using SFC in place of, or in addition to, HPLC is that it may offer different selectivity and thus has the potential for improved separation success rates. In this paper, we examine relative success rates for SFC and HPLC in obtaining adequate selectivity for successful separation. Our results suggest that use of SFC in addition to HPLC may result in a slight (1-2%) improvement in success rate compared to use of HPLC alone.