A method of determining a fluid level in a well space without substantial venting of gas to the atmosphere or injecting a gas at high pressure. Gas being produced by the well is used to create a pressure differential between two spaces. A wave is induced in the well space by causing the two spaces to come into gaseous communication for a selected time internal. Pressure changes are measured as the induced wave travels through the gas in the well space from the measurement system to a fluid surface and back to the measurement system to determine a round trip travel time of the wave. The fluid level is calculated from the round-trip travel time and a speed of the wave as one-half of the product of the wave speed and the round-trip time.