This paper presents work towards a gas sensor based on surface enhanced Raman spectroscopy (SERS). Sensitive SERS analysis of CO and N(2)O was performed using a mixed AgPd nanoparticle substrate that facilitated effective gas adsorption and strong SERS generation. The adsorption, desorption and displacement of both gases from the AgPd substrate were studied. We find that heating/cooling of the AgPd is necessary for CO adsorption but after this step a maximum SERS enhancement factor (EF) of 4 x 10(5) was measured and subsequent desorption and displacement occurred readily. For N(2)O, adsorption occurred at ambient temperature and the maximum SERS EF was 1 x 10(5), but desorption required heating and CO would not displace N(2)O from the surface but was rather co-adsorbed. We conclude that it is necessary to ensure analytes adsorb relatively weakly to the SERS substrate to enable continuous, real-time analysis of multiple analytes and to avoid substrate contamination.