The information to be provided to consumers (known as the mix) is presented in terms of the percentual contribution of each energy source to the total energy sold by the supplier.

The categories of energy sources that suppliers must take into account when calculating their mix are:

• Wind: production of electricity using wind resources (namely wind generators)
• Hydropower: production of electricity using the flow or difference in level of watercourses, regardless of size and remuneration scheme
• Renewable cogeneration: combined production of thermal energy and electricity, using non-fossil resources as fuel
• Geothermal energy: production of electricity using geothermal resources
• Other forms of renewable energy: production of electricity based on renewable energy sources other than wind power, hydropower or renewable cogeneration, including solar energy, wave and tidal power, biomass and biogas
• Municipal solid waste: production of electricity using municipal solid waste as fuel
• Fossil cogeneration: combined production of thermal energy and electrical energy, using fossil resources as a fuel
• Natural gas: production of electricity using natural gas as fuel in combined cycles (steam and gas turbines)
• Coal: production of electricity using coal as fuel in steam cycles
• Diesel: production of electricity using diesel or fuel oil as fuel in diesel cycle engines
• Fuel oil: production of electricity using fuel oil as fuel in steam cycles
• Nuclear: production of electricity using nuclear fission

The information must be presented by each supplier to its customers and potential customers.

Suppliers are required to inform consumers about the labelling of electricity using the following media:

• Invoices sent to the customer
• Supplier’s website with an area dedicated to labelling
• Standardised contract form for each commercial offer, as set out in the Commercial Relations Regulation (Regulamento de Relações Comerciais - RRC)
• Annual leaflet

Suppliers, the transmission and distribution concessionaire of the Autonomous Region of the Azores and the transmission concessionaire and bound distributor in the Autonomous Region of Madeira must present the following information on invoices to consumers, on a quarterly basis, by the 15^th day of third month after the quarter concerned (q + 3 months), in relation to the previous quarter, in a clear manner, with accessible language, and using carefully designed graphics with the following information:

• Offer mix or, where the mix is not differentiated according to the offer, the supplier’s mix
• Value of total CO₂ emissions relative to the invoice’s consumption
• Hyperlinks to the labelling sections of the supplier’s and ERSE’s websites (preferably active in the case of electronic invoicing)
• In the case of an invoice adjustment, in which the values already invoiced show a negative difference between the consumption of the invoice in question and that of previous invoices, and the calculation of CO2 emissions is negative, an explanation similar to the following text should be included: “The negative value results from the adjustment of previous invoices”, next to the value of CO2 emissions
• In the case of the “conta certa” type of contracts, the information regarding CO2 emissions must be provided in the invoice issued at the end of the period to which it relates and must correspond to the total consumption in that period.

Suppliers should maintain an area dedicated to labelling on their website, permanently updated, with the following information:

• Supplier mix in the last quarter
• Evolution of the supplier mix up to the last 4 quarters
• Mix of each offer in the last quarter, except where offers do not have at least one quarter of reporting history
• Value of specific CO₂ emissions of the supplier’s offers in a given year, if applicable
• Value of the supplier’s specific CO₂ emissions in the last year
• Additional information on environmental impacts, including the following information:
• General information according to the format made available by ERSE;
• Intra-organisational measures implemented by the supplier to reduce environmental impacts and not reflected in emission figures previously published.

• Emissões específicas da oferta do comercializador 
  O comercializador calcula, anualmente, as emissões específicas de CO₂ de cada oferta adicionando os fatores de emissão de cada fonte de energia emitente, de categoria c, ponderados pela sua contribuição para o mix da oferta do comercializador, relativas ao último trimestre do ano anterior.
• Emissões específicas do comercializador
  O comercializador que opte por apresentar um mix genérico, calcula anualmente, as emissões específicas de CO₂, adicionando os fatores de emissão de cada fonte de energia emitente, de categoria c, ponderados pela sua contribuição para o mix do comercializador, relativas ao último trimestre do ano anterior.
• Emissões totais de CO₂ associadas ao consumo da fatura
  As emissões totais de CO₂ associadas ao consumo de uma fatura são calculadas pelo comercializador que emite a fatura e variam consoante a opção de mix a apresentar.

The standardised contract form, provided for in article 105 of the Commercial Relations Regulations for the Electricity Sector, must include the following information:

• Mix of each offer in the last quarter, except where the offer does not have at least one quarter of reporting history;
• Supplier mix in the preceding calendar year or, where the supplier was not active in the last calendar year, the mix of the last quarters;
• Value of the supplier’s specific CO₂ emissions in the last year.

Whenever the supplier presents a commercial offer to a potential customer, it must deliver the respective standardised form and the most recent annual leaflet.

The annual electricity labelling leaflet, sent to customers (by post or email) by the end of May, must provide the following up-to-date information:

• Supplier mix in the previous calendar year
• Value of the supplier’s specific CO₂ emissions in the last year
• Additional information on environmental impacts, including the following information
• General information according to the format made available by ERSE
• Intra-organisational measures implemented by the supplier to reduce environmental impacts and not reflected in emissions figures previously published
• Hyperlinks to the supplier’s and ERSE’s websites areas on labelling (which should ideally be active, in the case of electronic invoicing).

Suppliers are allowed to make electricity offers with specific and differentiated characteristics as regards their origin, presenting a different mix for each of these offers (specific mix), which reflects the different preferences of their customer portfolio and their commercial market approach options.

This item falls under the responsibility of the supplier, if it wish to do so. This assumption recognizes the need for suppliers to identify, in the area that concerns labeling, measures adopted internally by them to reduce environmental impacts.