Thin films of functionalized single-wall carbon nanotubes were deposited on silicon chips by drop-coating and inkjet printing. These sensors were subjected to 1-100 ppm NOx, CO, H2S and H2O vapor in synthetic air. We have found that besides the expected changes in the electrical resistance of the film, there are also characterteristic differences in the noise pattern of the resistance vs. time function. This phenomenon is called fluctuation enhanced sensing and it can be used to increase the amount of information gathered from a carbon nanotube sensor device. The main advantage of fluctuation enhanced sensing is the improved selectivity of the sensor even if changes in electical resistance are rather low. Combined with differentiation based on modifying the adsorption characterstics of the nanotubes (e.g. by covalent functionalization), fluctuation enhanced sensing appears to be a very useful method for bringing cheap and reliable carbon nanotube based chemical sensors to the market.