In the Cerro Prieto geothermal field (CPGF) the steam from producing wells is transported to the power plants through a large and complex system of pipes which are thermally insulated with a 2" thick mineral wool or fiber glass layer and an external aluminum or iron cover. After a long time of field operation, the insulation has been exposed to weather conditions and has suffered density and thickness changes, and has even been completely lost in some cases, causing an increased heat transfer from the pipes to the environment. In this work, the impact of thermal insulation condition on the heat losses in the CPGF steam pipeline network is analyzed. Then, the heat losses per unit length are calculated by applying an iterative method which determines the surface temperature based on a heat balance considering the three basic mechanisms of heat transfer: conduction, convection and radiation. Finally, based on the results of an inventory of the thermal insulation condition throughout the pipeline network, as well as field operation data, the overall heat losses throughout the pipeline thermal insulation are quantified. The results allowed us to compare the magnitude of these heat losses with the overall energy losses taking place during the steam transport from wells to the power plants and, this way, to evaluate the impact of not having insulations in a good condition.