The energy markets are currently under tremendous pressure caused by instability in fuel prices and environmental issues. The citizens are affected by the constant increase in fuel prices, threat to the security of energy supply and by climate change resulting from an environmental policy neglected So, cogeneration systems arise as a way of producing high efficiency energy, lower environmental impacts, and a decrease in the consumption of primary energy. However, cogeneration, to date recognized as one of the most efficient ways of producing electricity and thermal energy, has seen its future in jeopardy because of the recent austerity policies which have decreased the remuneration regarding the electricity produced. The objective of this work is the approach to the new legal framework applicable to the cogeneration activity in Portugal. In that way, an energy audit was done based on an existing cogeneration plant. A comparison of the results obtained by applying the new legal framework with the results obtained by previous legislation was carried out. The avoided CO2 emissions were compared with separate heat and electricity production. A sensitive economic analysis was carried out in function of the prices of electricity, fuel and cost investment.