We reproduced the chemical-physical conditions of fumarolic emission at Phlaegrean Fields, Pozzuoli, Italy, and we measured the C[O.sub.2] and [H.sub.2]O concentrations using an absorption spectrometer based on two distributed feedback laser diodes at wavelengths of 1.578 and 1.393 [[micro]meter]. We discuss the accuracy levels of the different methods used. Furthermore, we measured the broadening coefficients for [H.sub.2]O (self-broadening, 28.2 [+ or -] 0.6 MHz/Torr; C[O.sub.2] broadening, 6.0 [+ or -] 0.4 MHz/Torr) and C[O.sub.2] (self-broadening, 3.2 [+ or -] 0.1 MHz/Torr; [H.sub.3]O broadening, 4.0 [+ or -] 0.1 MHz/Torr). Using the present data, we evaluated a minimum detectable variation of 9% for [H.sub.2]O and 1% for C[O.sub.2]. Key words: Environmental spectroscopy, molecular spectroscopy, near-infrared gas sensing.