INTRODUCTION The following report details the results of exposure tests performed on elastomeric materials used in well head equipment. The program was conducted for the American Petroleum Institute (API) by cortest Laboratories@ Inc. (CLI) between September@ 1991@ and March@ 1992. The API project on elastomer test methods was conducted in two parts. The objective of the first part was to determine the effect of fluid composition on the performance of a single elastomeric material (Sulfur cured Krynac 3850 - NBR). The results of Task A were reported in June of 1991. The data allowed the selection of a preferred fluid (90/10 isooctane/toluene) which was used in the test program reported here. In Task B the properties of five elastomer compounds were measured after exposure to the hydrocarbon test fluid chosen in Task A. The isooctane/toluene was in equilibrium with two gas compositions and at three temperatures. The objective of Task B was to determine the sensitivities of the various materials to environmental constituents (H2S@ CO2)@ temperature@ liquid phase composition and exposure duration. Additional testing was performed to determine the effect of temperature@ pressure and solvent without chemical interactions from H2S or CO2. These data allowed chemical effects from gases or solvents to be separated from the effects of temperature or pressure degradation. The test program supported efforts by API Task Group 6A to standardize test procedures for elastomeric materials. The materials of interest are elastomeric and are intended for use in pressure bearing components@ primarily as seal materials in oil field production equipment. In service@ these materials are exposed to produced and injected gases and fluids. The general approach to elastomer evaluation is to measure physical and mechanical degradation produced by exposure to a simulated produced fluid (gas@ hydrocarbon liquids) environment.