A detailed description of the construction, calibration and operation of 4 open-circuit chambers designed to measure methane emissions from sheep is given. These chambers have accommodated sheep under ad libitum feeding and have been used in short-term experiments and over extended periods of time. A real-time base data acquisition and process control system provided 24 h operation of the methane chambers. The gas volume measurement system consisted of dry test meters and sensors for differential and absolute pressure, temperature and relative humidity. This enabled correction of methane chamber exhaust air volume to standard temperature and pressure. Temperatures and relative humidity during measurements ranged from 21.0 to 23.1°C and 53.8 to 78.9%, respectively. The gas chromatograms were calibrated 3 times a day using commercially available gas standards. Recovery tests were conducted on each chamber by bleeding a methane gas standard into the chamber at a rate similar to methane production by sheep, with 94.4–107.1% of the methane gas recovered. Measurements on 32 sheep gave methane emissions within predicted levels and identified several low methane-producing sheep.