We describe a new technique for measuring the infrared absorption spectra of gases using atomic force microscope microcantilevers. This photoacoustic system is demonstrated for a dilute acetylene/helium mixture by recording the acetylene ν₁+ν₃ infrared overtone transitions using a wavelength modulated tunable diode laser as the infrared light source. The technique presents significant advantages over existing methods in terms of size, simplicity, speed and insensitivity to ambient vibrations. The maximum achievable signal-to-noise for resonant and non-resonant photoacoustic excitation of the microcantilever is examined and is found to be limited by the microcantilever’s Brownian noise.