A method of testing for leaks in a contained system with an interior containing system gas and system liquid at an operating pressure, the method comprising: pressurizing the interior of the contained system, by introduction of gas comprising tracer gas into the interior, to at least 0.5 pounds per square inch above the operating pressure to disperse the tracer gas throughout the system liquid; and sensing for the presence of the tracer gas using one or more sensors located outside the contained system.