f. The fourth step is subtraction of the amount of carbon stored in products for long periods of time (e.g., non-energy uses). The Reference Approach requires information on the consumption of fuels used for non-energy purposes where carbon may be stored (i.e., not oxidized and emitted to the atmosphere). The Reference Approach uses a simple assumption: once carbon is brought into a national economy in the form of a fuel, it is either saved in some way (e.g. in increases of fuel stocks, stored in products, or left unoxidized in ash) or it is emitted to the atmosphere.

Some of the fuels supplied to an economy can be used for non- energy purposes or as raw materials (i.e., feedstocks) for the manufacture of products. A wide variety of products are produced from oil refineries, including asphalt and bitumen for road construction, naphthas, lubricants, and others for production of plastics and fertilizers. Natural gas is used for ammonia production. Liquid petroleum gas (LPG) is used to produce solvents and synthetic rubber. By-products of the coking process, oils and tars, are used in the chemical industry. In some of these cases the carbon in these fuels is oxidized to CO₂ within the non-energy process (e.g., carbon from natural gas used in ammonia production). In other cases the carbon is indefinitely stored (i.e., sequestered), although the carbon in some products may be oxidized as the product ages or is disposed of. The amounts stored for long periods are called stored carbon and should be deducted from the carbon emissions calculation.

Several approaches for estimating the portion of carbon stored in products are reviewed in the 1996 Revised IPCC Guidelines. It recommends that, whenever possible, Parties should use country-specific data and assumptions instead of relying on IPCC default fractions of carbon stored.