The preferred seal gas supply method for tandem seals is currently with differential pressure control above a reference pressure. Measurement point options for the reference pressure include the seal balance line, the thrust balance line or a seal cavity port. When the system is supplying two seals, the supply flow to each seal can be balanced by installing an orifice in each of the individual supply lines. Individual flow indicators and throttling valves that are parallel to each of the restriction orifices can also be installed to provide some degree of adjustment. Valve arrangements that can completely cut off seal gas flow to a seal should be avoided. The proper set point range for the differential pressure control should be determined by the compressor and seal suppliers, based on the design of the compressor and seal gas labyrinths, the reference gas measurement point and optimization of the seal gas consumption rate. Additional considerations must be made for lower pressure services to prevent pressure reversals due to either venting system pressure excursions or vacuum conditions that can occur during compressor start-up. The seal gas supply control system should also include differential pressure alarms, and provisions for on-line maintenance of the differential pressure control valve (manual bypass with local DP indicator and isolation valves). Single seals can be similarly arranged.