Abstract Present methods of detecting gas leaks during testing of well heads, tubular goods, flowlines and even complete gas plants are woefully inadequate. If leaks are allowed to continue, the resulting high costs, both financial and in human life, can be disastrous. A unique method of leak detection is now being employed to record leaks as low as 0.0001 ce/sec (1 SCF in 10 years). With this innovative technology, the oil and gas industry is now able to eliminate the presence of dangerous gases to a degree not possible prior to this development. The process involves the use of a tracer gas (helium) and a portable mass spectrometer tuned to respond to the molecular weight of this gas. To date, the method has seen widespread use on production platforms in the North Sea, with outstanding success. Its reputation for providing a reliable and safe means of leak detection remains untarnished. Details of the process and up-to-date job histories will be presented in the paper. Introduction In today's petroleum industry, the demands on systems used in the transfer of hydrocarbons are rising steadily. Gas production facilities, chemical plants and oil refineries are operating more efficiently, and at higher capacities. Because these facilities deal with toxic and flammable gases at high pressures, safety standards require a high level of system integrity. This means leaks must be detected and repaired. Various methods have been used for leak detection, with limited success. Hydrostatic testing is not acceptable for establishing the leak integrity of a gas flow system due to the differences in gas and liquid flow regimes (Santeler/Moller(1)). Methane and H2S gas can closely simulate operating conditions, but the techniques and instruments used do not provide accurate and reliable results. The demand for a safer, more sensitive and quantitative method of leak detection led to the techniques described in this paper. The use of the helium mass spectrometer to detect leaks is not a novel idea-the technology has been available for over thirty years. Its use has been mainly confined to the high vacuum industry, with specialized applications in space simulation apparatus and nuclear breeder research. Initial development was tied in closely with the manufacture of mercury-are rectifiers and hermetically sealed meters for the aircraft industry. Work has progressed to include the testing of intermediate heat exchangers, as outlined by Hopkins(2) for use in liquid fast breeder facilities, but the methods used were centered around vacuum techniques. Pressurized systems, although as prone to troublesome leaks as vacuum systems, had never received the benefits of advancements in helium leak detection.