This paper presents a methodology to estimate the present Greenhouse Gas Emission Factors of the Argentinean electrical grid using current and historical generation information published by the Compañia Administradora del Mercado Eléctrico Mayorista S.A.. The methodology identifies the marginal sources of generation, proposes a way to estimate the current composition of the thermal generation component, and combines this information with generation data to estimate the values of the current Average and Marginal Emission Factors of the electrical system. Using this methodology a website was developed where the updated results are published with free and open access: www.emisionesdelared.ar