During late summer of 1993 a field study took place in Baytown, Texas, where a comparison was made between the Opsis open-path system and conventional point sampling monitors. Simultaneous measurements of the three criteria pollutants sulfur dioxide, nitrogen dioxide, and ozone were made during a time period of a month, including data on wind speed, wind direction, and temperature. This study was made in an area with numerous major local sources of pollution. The degree of agreement between the open-path system and the point measurement system depended on the gas being measured. Ozone, which is well mixed, showed very good intercomparison whereas SO2 showed poor intercomparison from time to time. By studying the discrepancies as function of the wind direction, interesting results were obtained.