The U.S. EPA Office of Air Quality Planning and Standards (OAQPS) has the responsibility for formulating regulations for the control of fugitive emissions of volatile organic compounds (VOC). 'Fugitive emissions' generally refers to the diffuse release of vaporized hydrocarbon or other organic compounds. Fugitive emissions originate from equipment leaks as well as large and/or diffuse sources. The study reported here was undertaken by the Office of Research and Development to assist OAQPS in the development of regulations. The project was designed to quantify the effectiveness of routine (on-line) maintenance in the reduction of fugitive VOC emissions from in-line valves. An overall emission reduction of approximately 70% was achieved by tightening the bolts on the valve packing gland. This level of control was sustained for up to about six months. The rates of leak occurrence and recurrence were also evaluated, as well as the time required to conduct the on-line maintenance.