The main object of this research was carry out technically a mass and energy balances in an energy cogeneration plant with cattle excrement gas a fuel composed by biogas + natural gas. This fuel was used like raw material for hydrogen production. Also to evaluate the economic pre-feasibility of the steam reforming plant using GN and Biogas + GN mixture fuels. An analysis of an electric energy cogeneration plant was realized, this plant will we biogas and GN. Based on these fuels an industrial scale for this research was fixed. An installed power of 75 MW was selected. Mass and energy balances were carried out over this installed power. Before carrying out the energy and mass balances biological reaction of the excrement was obtained. As a result chemical reactions in the steam reforming process were developed since 3 hypothesis as possible fuels in reforming were used. The mixture of 70% biogas + 30% GN obtained the same hydrogen production quantity (29.683.500 kg/year) with the use of 100% GN in the steam reforming process. Talking about the economic evaluation, the project profitability measured over the VPN and TIR economic indicators base was similar for the fuel mixture (biogas + GN) and GN fuel in the steam reforming process. It is important to notice that the variable costs showed the difference between the use of biogas + GN mixture and the use of GN, also the use of biogas. The results had a big difference in the unitary total cost.