A plurality of sensors of the same composition or different compositions are provided on a substrate or in a bundle and are sensitive to a plurality of constituent species in a mixed species medium being measured. The sensors of the same composition may each be maintained at different temperatures. The sensors of different compositions may each be maintained at the same temperature or different temperatures. The intersection of measurement values from the plurality of sensors may be used to determine the actual concentrations of the constituent species (e.g., hydrogen and oxygen) in the mixed species medium.