A method for determining a measure of a gas concentration from a group of at least two non-dispersive infrared. NDIR. gas sensors (S1-SN) is described. The method comprises the steps of obtaining. at a processing unit (1), from each NDIR gas sensor (S1-SN) a measure of a gas concentration as a belief function Pi(x), which provides a probability as a function of the sensed light intensity at a specific wavelength, merging. in the processing unit, the belief functions Pi(x) to a merged belief function P(x). A computer program performing the method is also described.