The work shown next deals with the definition of nodal marginal prices, in the context of an economic dispatch solution with transmission losses. The losses are incorporated through penalty factors obtained from line distribution factors, using a linearization process. This study is applied to the hydrothermal venezuelan system, considering plants with regulation capability and run-of-river dams. The objective function to be minimized includes present and future thermal costs. In addition, a discussion is given about the correct location of the slack node, in order to get similar results to these associated to an OPF solution. © 2006 IEEE.