Substantial and practical research as to the long-term viability and usefulness of continuous respirometers in on-line, field testing is scarce. A robust respirometric device of simple operation which yields valuable and consistent data would be valuable in the field of wastewater treatment. The OLR-300, a continuous on-line respirometer developed and manufactured by Challenge Environmental Systems, Inc., was installed at the Paul R. Nolan Wastewater Treatment Plant in Fayetteville, Arkansas. Oxygen uptake data of the biological system was monitored during the period of January 2006–September 2006. The purpose of this study was twofold: (1) to determine the limits of the OLR-300, including the machine's accuracy and reliability, frequency of maintenance, restrictions, and overall ease of usage, (2) to discover the overall usefulness of the machine thru the quality of information obtained and the correlation of this information with available operational data provided by the WWTP.