This paper examines the determinants of waterborne transport costs, with particular emphasis on the efficiency at port level. Its main contribution is (1) to generate statistically quantifiable measures of port efficiency from a survey of Latin American common user ports, and (2) to estimate a model of waterborne transport costs, including the previously generated port efficiency measures as explanatory variables. In order to incorporate different port efficiency measures from the survey, we use principal component analysis (PCA). Our estimations show that the specified variables in the model explain a great proportion of the change in waterborne transport costs. With regard to port efficiency, the result is especially important for one of the port efficiency measures obtained through PCA with an estimated elasticity equivalent to that of distance. Other explanatory variables which show to be statistically significant are the monthly liner service availability, distance, and the goods' value per ton. The conclusions are relevant for policy makers as they show and quantify that port efficiency is a relevant determinant of a country's competitiveness – and in this respect, there still exist big differences among Latin American countries. Unlike most other relevant variables, port efficiency can be influenced by public policies. Maritime Economics & Logistics (2003) 5, 199–218.