Natural gas provides more than one-fifth of all the primary energy used in the United States. Much raw gas is "subquality", that is, it exceeds the pipeline specifications for nitrogen, carbon dioxide, and/or hydrogen sulfide content, and much of this low-quality natural gas cannot be produced economically with present processing technology. Against this background, a number of industry-wide trends are affecting the natural gas industry. Despite the current low price of natural gas, long-term demand is expected to outstrip supply, requiring new gas fields to be developed. Several important consequences will result. First, gas fields not being used because of low-quality products will have to be tapped. In the future, the proportion of the gas supply that must be treated to remove impurities prior to delivery to the pipeline will increase substantially.1,2 The extent of treatment required to bring the gas up to specification will also increase. Gas Research Institute studies have shown that a substantial capital investment in facilities is likely to occur over the next decade. The estimated overall investment for all gas processing facilities up to the year 2000 alone is approximately $1.2 Billion, of which acid gas removal and sulfur recovery are a significant part in terms of invested capital.3 This large market size and the known shortcomings of conventional processing techniques will encourage development and commercialization of newer technologies such as membrane processes. Second, much of today's gas production is from large, readily accessible fields. As new reserves are exploited, more gas will be produced from smaller fields in remote or off-shore locations. The result is an increasing need for technology able to treat small-scale gas streams. Third, 80% of raw gas that is over specification in carbon dioxide also contains hydrogen sulfide.2 About 13% of presently known and predicted reserves are prone to hydrogen sulfide contamination.1 As subquality fields are exploited, the need for better, cheaper hydrogen sulfide removal and sulfur recovery processes will increasing. Finally, atmospheric discharge of sulfur compounds, either by venting or flaring, now commonly used, will be increasingly regulated for environmental reasons.