In the calculation of the main sources of sulphur dioxide emissions, the combustion processes associated with the use of liquid fuels derived from petroleum assume a very considerable weight, so that the regulation of the maximum allowed sulphur levels of these fuels is an effective measure in order to avoid adverse effects on human health  and the environment. These emissions of sulphur dioxide include emissions from ships resulting from the burning of marine fuels with a high sulphur content, which contribute to air pollution in the form of sulphur dioxide and others particles that harm human health and the environment and contribute to acid rain.

In order to reduce the emissions of sulphur dioxide resulting from the combustion of certain types of liquid fuels, including heavy fuel oils, bunker fuel oils and marine gas oils, thereby reducing the harmful effects of these emissions on human health and the environment, it has been adopted, on 26 September 1997, by the International Maritime Organization (IMO), the 1997 Protocol relating to the International Convention for the Prevention of Pollution from Ships, 1973, as amended by the 1978 Protocol, MARPOL 73/78, which included a new Annex to MARPOL 73/78, the Annex VI, which was approved by Decree No. 1/2008 of 9 January.

This new MARPOL Annex sets limits for sulphur oxide and nitrogen oxide emissions from ships and prohibits the deliberate release of substances that deplete the ozone layer. The Annex sets an overall limit of 4.50% of sulphur content of the fuel oil. In the light of similar concerns, the Council adopted Directive 1999/32/EC of 26 April 1999 on the reduction of the sulphur content of certain liquid fuels and amending Directive 93/12/EEC, which transposed into national law the Decree-Law No. 281/2000 of 10 November.

The objective of Directive 1999/32/EC was to incorporate the rules adopted by the International Maritime Organization (IMO) into EU legislation, with the aim, inter alia, of strengthening the international monitoring and implementation regime. This Directive 2005/33/EC of the European Parliament and of the Council of 6 July 2005, was transposed by Decree-Law No. 69/2008 of 14 April, which introduced into European Union framework, inter alia, others IMO provisions on Sulphur Emission Control Areas (SECA) and maximum sulphur levels of the most restricted marine fuels.

Directive 1999/32/EC of 26 April 1999 was further amended by Directive 2009/30/EC of the European Parliament and of the Council of 23 April 2009 as regards the specifications of fuels used in inland waterway vessels, which was transposed by Decree-Law No. 142/2010 of 31 December. On 10 October 2008, the IMO adopted the revised Annex VI, through Resolution MEPC.176 (58), which entered into force on 1 July 2010.

The revised Annex VI introduced, in particular, stricter maximum limits for the sulphur content of marine fuels in SECA (1,00% as of 1 July 2010 and 0,10% as of 1 January 2015), as well as in other sea areas outside the SECA (3,50% as of 1 January 2012 and 0,50% as of 1 January 2020).

Directive 2012/33/EU was transposed into the internal legal order by Decree-Law No. 170-B/2014 of 7 November, which introduces the third amendment to Decree-Law No. 281/2000 of 10 of November, as amended by Decree-Laws No. 69/2008 of 14 April, and 142/2010 of 31 December. In order to achieve the objectives of Directive 1999/32/EC, as amended, the EU recognized the need for a strengthened regime for monitoring the provisions of the Directive.

To this end, Member States shall ensure a sufficiently precise and frequent sampling of marine fuels placed on the market or used on board vessels, and shall also ensure the regular monitoring of the ship's logbook and the fuel delivery guides.

In order to ensure a fair sharing of the costs between Member States and a cost-effectiveness, as well as specific alerts for certain vessels, the Commission adopted Implementing Decision (EU) 2015/253 of 16 February 2015, laying down rules for sampling and reporting in the framework of the Directive 1999/32/EC of the Council on the sulphur content of marine fuels. For reasons of consistency with international regulations and to ensure that the new world-wide standards of sulphur content are properly monitored in the EU, the European Parliament and the Council adopted on 21 November 2012 Directive 2012/33/EU, which amended Directive 1999/32/EC in order to align EU legislation with the revised Annex VI of the MARPOL Convention.

 List of Naval Fuel Traders
In compliance with the Article 4.º-A (a)(10) of Decree-Law No. 281/2000 of 10 November, amended and republished by Decree-Law No. 170-B/2014 of 7 November, is available at the institutional portal of the ENMC - National Entity for the Fuel Market, EPE, the Naval Fuel Suppliers List (updating).