approach is twofold: to help government officials and citizens understand the overall scale of public spending and policies promoting particular energy pathways, and to help identify the most important leverage points for reform. An inventory would ideally cover all direct expenditures by the government, forgone revenues due to targeted tax and other fiscal concessions, and potentially many other forms of support, including below-market provision of credit and insurance, MPS to producers, and market transfers to or from consumers. A detailed exposition on the accounting framework for producer support estimate (PSE) and consumer support estimate (CSE), with illustrative calculations in agriculture, can be found in OECD (2010b). Examples of measures supporting fossil fuels include budgetary transfers to an oil price stabilization fund or to state-owned natural-gas utilities; sales of subsidized crude oil by a national oil company to a state-owned refinery; a tax holiday, credit guarantees, or a subsidized loan for a new natural gas pipeline project; and priority access to the grid for electricity generated by a utility in financial trouble. Particularly informative compared with the sole use of a price gap is the full quantification of producer subsidies, consumer subsidies, or both, that an inventory approach enables. Case studies for energy can be found in Koplow and Charles (2010) and Koplow and Lin (2012). For agriculture, _OECD Review of Agricultural Policies_ has numerous examples, not only for the OECD countries but also for seven countries outside of the OECD (www.oecd.org/tad/agriculturalpolicies/producerandconsumersupportestimatesdatabase.htm#country).

Even qualitative listings of support measures add value, because market distortions can be seen more clearly and examined once interventions are identified. The qualitative information can be expanded and quantified over time. For this reason, starting with a comprehensive list, even if many entries are blank for lack of data, can be informative, in particular for policy makers seeking to reform fossil fuel subsidies.

The framework developed by the OECD to produce its inventories of transfer mechanisms provides a strong starting point. Policies of primary support to individual producers are grouped into the PSE and those to individual consumers into the CSE. Policies that benefit producers or consumers collectively, or that do not necessarily support current production or consumption, are grouped under the general services support estimate (GSSE). Examples of the GSSE include rehabilitation of lignite mining sites in Germany; government assumption of inherited environmental liabilities for coal mining in the Republic of Korea; and public funding for basic, fossil-fuel-related R&D. The OECD combines PSE, CSE, and GSSE to arrive at the TSE, with some adjustments to avoid double-counting.

This framework, if carried out comprehensively, may be considered a unified framework covering all measures of subsidies. All price gaps would be captured as transfers to consumers (from tax payers, producers, or both) or to producers (from tax payers, consumers, or both). Additional forms of subsidies, such as cash transfers to consumers to pay for fuel purchase or tax breaks for producers, would be captured as CSE or PSE. The OECD has been compiling these data for agriculture since the mid-1980s and for fisheries since the late 1990s. The coverage in agriculture is broad, covering virtually everything that this paper defines as a subsidy.

The OECD began tracking for fossil fuels in 2010. To date, the OECD has included in its _Inventory_ mainly those measures that have been obtained from published government sources. Due to data limitations, 24