Although in the last few years at both national and European level a number of documents have been put forward on the great opportunities offered by the development of the ‘Motorways of the sea’ in re-directing freight flows, there is a lack of any empirical analysis on the determinants of such choice by operators. In other words, a lot has been done in analysing supply and very little in analysing demand. Identifying the value that users assign to the specific transport alternative would strongly contribute to evaluating the possibility of a tradeoff between the maritime short sea shipping (SSS) mode and the other modes. Furthermore, the identification of the factors related to both the mode and the specific organisation of the companies that exert a significant influence on the choice of operators and the magnitude of their impact would represent, in such instances, a necessary prerequisite for any forecasts. In the last decade significant improvements have been made in the definition of a methodology capable of realistically interpreting the decision-making process of operators with respect to transport service choice, especially when facing only potential alternatives. Using a methodology falling within the broad definition of conjoint analysis – the adaptive stated preferences approach – we measure the trade-offs among service characteristics that shippers make when evaluating the Ro-Ro option (already present on the market or still hypothetical) against surface alternative services. The paper is based on data collected through questionnaires and direct interviews carried out on a sample of operators located in the north-western regions of Italy. Given the characteristics of the data-base, the estimation has been carried out using a tobit model.