Phase-shift cavity enhanced absorption spectroscopy has been described for the case of an off-axis alignment of an optical cavity formed by high reflectivity mirrors. The effect of laser broadband amplified spontaneous emission (ASE) from a DFB diode laser (similar to 1605 nm) has been analysed for absorption measurements extracted from the phase-shift of the intensity modulated beam. A simple model has been proposed for extraction of actual absorption spectra and linestrengths from the phase and amplitude measurements. It has been shown that omitting the ASE contribution to the cavity output light intensity may lead to an overestimation of absorption linestrength. (c) 2006 Elsevier B.V. All rights reserved.