A survey of guests at 6,850 hotels in Spain found that the guests gave higher satisfaction ratings to hotels that held the ISO 14001 certification than to hotels without the certification. As an international standard aiming at development of effective environmental management systems, the ISO 14001 standard specifies a path for the continuous improvement and the control of a firm’s environmental performance. The study explored the differences in the overall customer ratings for the certified hotels overall and for several individual services and attributes, including housekeeping and overall comfort. Interestingly, the most significant differences were found between upscale 4-star hotels with and those without certification, while differences relating to certification in 5- and 3-star hotels were muted. While the study does not reveal causes for these findings, the implication is that the highest-end luxury hotels do not gain distinctive differentiation by having the ISO 14001 certification, while for 3-star hotels, guests’ price sensitivity apparently overrides environmental concerns. That said, the results imply that acquiring ISO 14001 certification may give upscale hotels a distinctive asset that leads them to a competitive advantage over similar non-certified properties. Moreover, ISO 14001 seems to contribute to the value creation by the hotels, based on their higher guest ratings.