The characteristics of surface plasmon wave (SPW) modes supported by multiple layer configurations are analysed in this paper. The transmission-line analysis based on the transverse resonance condition is implemented to describe SPW excitation via a prism coupler. This accurate yet convenient modeling technique is also applied to investigate the characteristics of SPWs in multilayer media with optical gain as a means of reducing/overcoming the typical, undesirably large loss associated with SPWs in conventional structures. The paper will also present experimental and theoretical results to quantify the operational characteristics to be expected from prism coupled SPW sensors that use semiconductor optical sources.