The X factor in price cap systems is useful to identify the inefficiencies of the costs of port services. However its determination can be controversial and rife with risks due to the asymmetry of information. In this article, a model is proposed to set the X factor with the maximum tariff schema based on the Data Envelopment Analysis (DEA). With this tool it is possible to estimate the efficiency rate of the different elements of a group of decision units by comparing their supply levels and visible products for the State regulatory agency. In the case of port infrastructure it is possible to analyze the efficiency of the technology and the time investment of the ports according to declared costs, so that the efficient ports can have their costs approved, while the rest would have their costs reduced according to their efficiency rate.