The Republic of Bulgaria joint the UN Framework Convention on Climate Change (UNFCCC) in 1992 in Rio de Janeiro. The Parliament ratified the UNFCCC in March 1995. As an Annex I party to Convention, Bulgaria is obliged to conduct annual inventories on greenhouse gas (GHG) emissions by sources and removals by sinks using the GHG inventory methodology approved by the UNFCCC.

The inventories issuance started with the country base year – 1988. The first inventories covered the period 1988 – 1994. The annual GHG inventories for the period 1995 - 1997 followed the actual IPCC Guidelines on National GHG Inventories, 1995 and the results were published in the I-st and II-nd National Communications on Climate Change and in the National Action Plan on Climate Change. The GHG Inventories for 1998 and 1999 followed the Revised 1996 IPCC Guidelines, adopted as a basic methodological act for GHG emissions assessment by the UNFCCC. Since 1998 inventory data and results have been presented in the new Common Reporting Format (CRF).

The National GHG Inventory Report for the year 2002 presents the results from the inventory of the basic GHGs – carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), GHG precursors (NOx, CO, NMVOCs) and sulphur dioxide (SO₂), and the emissions of Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs) and Sulphur hexafluoride (SF₆).

The base year for the emissions of HFCs, PFCs and SF₆ is 1995. The GHG emissions for the period 1988 – 2001 were recalculated in accordance to some changes in data for emissions factors and parameters.
The structure and content of the National Inventory Report was updated according to the recommendations of the international experts’ team from the UNFCCC Secretariat during the In Country Review held in Sofia (1-5 September 2003).

The National Inventory Report was elaborated following the recommendations of the UNFCCC Guidelines pertaining to GHG inventories of Annex I Parties to the UNFCCC, adopted by the Conference of the Parties at its eight session held in 23 October – 1 November 2002 in New Delhi.