In electrical distribution systems, one of the greatest challenges for utilities is the estimation of technical losses. According to the literature, energy losses throughout the world s electric distribution networks may vary from country to country approximately between 3 percent and 25 percent of the electricity provided, which may cause great impacts on the electrical system costs. Specifically in Brazil, the appropriate evaluation of the energy losses provides valuable information for the regulator to establish the energy distribution tariffs. In literature, there are different ways for estimating energy losses, but due to the difficulty for modeling precisely the equipment of the system, as well as the lack of information regarding the energy consumed of each load, the energy losses estimation may lead to huge errors. To deal with this problem, it is proposed a new method based on a modified load model, taking into account the measurements of voltages and power at the substation and, when available, the measurements of voltages and power demanded by loads with meters installed. The main contribution of the proposed method is the use of the network information and the correlation between the power consumed by the loads and the voltage and power supplied by the substation. In order to detail and analyze the performance of the proposed method, three electric systems are used. The results of the estimations given by the proposed method are compared to those obtained with other methods found in literature and in practical applications.