Transportation Control Plans (TPC's) promulgated by EPA in 1973 and 1974 include requirements for the control of gasoline vapors at service stations in some 17 Air Quality Control Regions (AQCR's) throughout the nation. In all cases, control of gasoline vapors during storage tank filling (Stage I sources) is required. In many areas, control of vehicle fueling (Stage II sources) is also required. For storage tank filling, EPA regulations prohibit the release of more than 10 percent by weight of displaced organic vapors. While Stage I vapor control systems are relatively new, there has been substantial testing which shows that compliance with prescribed limits can ,be accomplished at commerical service stations: Tests by oil companies, EPA, and a local control agency indicate that efficiencies greater than 90 percent are effected with simple balance systems if certain common design elements are employed and if the equipment is properly maintained and operated. Based primarily on this testing, criteria have been developed for Stage I control systems. The purpose of this document is to provide direction to operators who are required to install vapor recovery systems.