The use of diode lasers in fibre optic gas sensors have been demonstrated and it is shown that instrumental drifts can be much reduced or totally eliminated to provide noise limited accuracy. The sensitivities obtained with these diode laser - fibre optic gas sensors are much higher than the sensitivity of the fibre-optic gas sensors utilising broadband radiation sources. The sensors are capable of detecting absorption directly or the photoacoustic signal produced in a resonant cell using a Mach-Zehnder fibre interferometer. For gases with strong absorptions in the near infrared, like HF, ppb level sensitivities have been obtained. Finally the ability of the instrument to make multicomponent gas analysis has been demonstrated.