This paper investigates the factors that influence the value for the users of the Portuguese electronic scientific information consortium b-on (Biblioteca do Conhecimento Online). We used the contingent valuation method based on a willingness to pay scenario to estimate the value that each user is willing to pay. Data were collected through an e-survey sent to all Portuguese academic users. The main aims of this study are: (1) to investigate whether the willingness to pay is influenced by a set of factors (the frequency of use, whether the user previously knew b-on or not, the type of the user, the scientific area of the user, and the institution of the user); and (2) to estimate the demand function of b-on services as function of the price and the previously mentioned factors. In order to achieve these objectives we use several regression analysis techniques--OLS, Tobit model, linear probability model (LPM), Logit and Probit models. The results show that the factors studied are all important explanatory variables of the willingness to pay for b-on and important determinants of demand for b-on services. Moreover, the demand for b-on services is quite sensitive to the "price". (Contains 8 notes, 3 tables and 1 figure.)