A fast response Wobbe meter for natural gas is described. The working principle of the Wobbe meter is based on a relationship between the Wobbe index, the concentration carbon dioxide and nitrogen and the specific density of natural gas. The concentrations are determined by Raman spectroscopy. A HeNe laser serves as the light source which generates Raman scatter in a cuvette filled with natural gas. A part of the scattered light is picked up and passed by two fibre optic cables to detection equipment. Filters are used to the allow N2 Raman light respectively CO2 Raman light to pass. The power of the light passing the filters is determined by photomultipliers. The concentrations are calculated from the power of the Ramen light signals, the pressure and temperature of the gas flowing through the cuvette, the laser power and callibration data. The accuracy of the concentration meters is better than 0.25% (gas 100%). This figure can be attributed to the statistical fluctuations of the intensity of the Raman light and to the way of estimating the background of the light signals. The response time is only 8 seconds. The accuracy of the Wobbe meter is better than 0.25 MJ/m3 which is good enough for a control instrument.