A method and apparatus for measuring volume correction in a gas pipeline using a variable volume chamber where the gas is sampled at the temperature and pressure of gas in the pipeline. A portion of a known volume of sample gas is released and a change of volume in the sample chamber is measured with respect to time, while maintaining temperature and pressure at pipeline conditions. The sample gas is then measured for molar flow rate at near base conditions, and this is used to calculate the molar density of the gas. Because the molar density of the gas has been measured at pipeline conditions, it can be multiplied by volumetric flow rate in the pipeline to provide base volumetric flow rate of the pipeline gas. A heating analyzer is provided to determine heat content of the gas, and this is multiplied by volumetric flow rate to determine energy flow rate.