The report gives results of analyses of 1985 industrial sulfur dioxide (SO2) emissions from two data sources: the National Acid Precipitation Assessment Program (NAPAP) inventory and the EPA TRENDS report. These analyses conclude that the two data sources estimate comparable emissions in the aggregate, but that estimates for specific categories and for processes within those categories vary widely. The TRENDS method, limited to source categories that emit 10,000 tonnes of SO2 per year, generally overestimates emissions from these source categories, due primarily to the absence of SO2 control efficiency assumptions. Overestimating emissions in the TRENDS data set is offset by including additional source categories in the NAPAP inventory, with the final aggregate estimates with < 10% of each other. Due to these findings, the TRENDS methodologies are being revised for 1993 and thereafter, using the 1985 NAPAP inventory as a base.