Economic valuation of ecosystem services by stated preferences techniques is usually used by policy-makers to develop environmental management practices. Critics of the contingent valuation (CV) method have argued that respondents are influenced by several factors, which mean that people do not apply economic motives in responding to CV questions. This study examines the influence of individuals' environmental behaviour and knowledge about the good concerned on the CV results and the CV problem of benefit aggregation in order to determine the extent of the hypothetical market. Here a CV study in the Doñana National and Natural Park (Spain) found that both individual environmental behaviour and knowledge influenced willingness to pay for sustaining specific ecosystem services provided by the biodiversity of Doñana. A distance-decay function was found, which determined the social benefits of the ecosystem services of Doñana. The study illustrates the importance of understanding non-economic motives behind values in order to obtain further information which can support decision-making in environmental management.