Recent studies have concentrated on environmental and economic impacts of ships. In this regard, fuel and C O 2 emission is considered as one of the important factors for such impacts. In particular, the sailing speed of the vessels affects the fuel consumption and therefore the emission directly. In this study, we consider a speed optimization problem in inland waterway, which is characterized by stochastic waiting times at the lock caused by uncertainty in lock processing time estimations of other vessels. The objective is to minimize fuel consumption of an approaching ship, such that it traverses the river segment in a set deadline. We introduce a mathematical model for this problem and evaluate the effectiveness and attractiveness of two solution approaches: an optimal solution and a simple heuristic. This creates intuitive guidelines for skippers based on information provision to select an appropriate speed decision approach to minimize the total expected fuel consumption and C O 2 emission of inland waterway transportation.