The Los Angeles Metro Rail project, begun as an 18-mile starter line (Figure 1), is now a 20-mile subway with 16 stations. At certain locations, the subway route will either skirt or cross old off fields. The presence of hydrocarbons due to oil deposits mandates that design consider the mitigating measures to limit the accumulation of subsurface gas to acceptable limits in the operation of the system. A ventilation system has been devised to remove such gases from tunnels and stations.