The fixed volum e expansion method for gas compressibility measurements previously employed under conditions of high temperature and high pressure has now been developed for low temperature and low pressure measurements. A sensitive diaphragm null-pressure detector, operating as a capacitor, has been incorporated into the gas pipettes, and eliminates troublesome dead space corrections. The advantages and limitations of the method are discussed. Measurements of the second virial coefficient of carbon dioxide in the temperature range −60 °C. to + 30 °C, and in the pressure range 0.5 to 2.5 atmospheres, are reported.