Multi-wall carbon nanotubes decorated by Ti nanoparticles were used for gas (N-2, Ar, O-2) sensing at low temperatures. Chemiresistor sensor configurations with supported and suspended nanotubes were tested. Two gas sensing mechanisms (chemical and electrothermal) were demonstrated, with their relative contributions strongly depending on the sensor configuration. For suspended nanotubes, heating by Joule effect results in strong enhancement of chemical sensitivity to oxygen. (C) 2009 Elsevier B. V. All rights reserved.