Which fuel line of the Intergovernmental Panel on Climate Change fits a blend of light diesel oil and furnace oil, or a fuel oil whose density I do not know?

The Intergovernmental Panel on Climate Change (IPCC) calls an oil residual fuel oil if its viscosity is above 10 centistokes at 80 degrees Celsius and its density always above 0.90 kilograms a litre. Furnace oil is about 0.96 and light diesel oil (LDO) about 0.85 on Petroleum Planning and Analysis Cell (PPAC) conversions, so a blend can cross the line.

The IPCC's own wording

• Residual fuel oil: it "comprises all residual fuel oils, including those obtained by blending". Its kinematic viscosity is above 0.1 square centimetres a second (10 centistokes) at 80 degrees Celsius, its flash point is always above 50 degrees and its density is always more than 0.90 kilograms a litre.
• Gas or diesel oil: includes diesel for compression-ignition engines, "light heating oil for industrial and commercial uses" and heavier gas oils sent to petrochemical plants.
• The IPCC names neither furnace oil nor LDO. Matching them to a line is a reading, not a quotation.

What PPAC's conversions say about density

PPAC's Ready Reckoner (Table 9.2) gives, per metric tonne at 29.5 degrees Celsius: furnace oil 1.0424 kilolitres, light diesel oil 1.172, diesel 1.2100. Dividing, that is 0.959, 0.853 and 0.826 kilograms a litre. Multiplying those volumes by PPAC's corrections to 15 degrees (0.9899, 0.9877, 0.9879) gives 1.0319, 1.1576 and 1.1953 kilolitres a tonne, so 0.969, 0.864 and 0.837 kilograms a litre. The IPCC does not state a temperature for its 0.90, but at either temperature furnace oil sits above the line and LDO below it.

A blend: where the density line is crossed

Our arithmetic, assuming the two volumes simply add: density 0.90 is reached at (0.90 minus 0.8532) / (0.9593 minus 0.8532) = 0.44, so about 44% furnace oil by volume, using the 29.5 degree densities. A blend lighter than that fails the density test for residual fuel oil; a heavier one passes it. The IPCC sets no density test for gas or diesel oil. The IPCC wording "including those obtained by blending" points to residual fuel oil for a blend made from furnace oil. That is a reading, not an IPCC statement, and the supplier's viscosity at 80 degrees decides.

Density is only one of the tests. Viscosity at 80 degrees cannot be worked out from two densities, so ask the supplier for the blend's density and viscosity on the delivery certificate, then pick the line that both numbers fit.

What a wrong line costs

Per kilogram the two lines are close: gas or diesel oil 74,100 x 43.0 = 3.186 kilograms of carbon dioxide (CO2), residual fuel oil 77,400 x 40.4 = 3.127, a gap of 1.9%. The big error is working per litre. Furnace oil is about 3.00 kilograms of CO2 a litre at PPAC's 29.5 degree density (3.127 / 1.0424) and LDO about 2.72 (3.186 / 1.172), at the 29.5 degree volumes. A diesel figure of 2.645 per litre used on furnace oil litres leaves out about 12%. Senseible's standard factor for furnace oil is 2.97 per litre at an assumed 0.95 kilograms a litre, so the shortfall is about 11% to 12% depending on the density used.

Example: 10,000 litres of furnace oil

• Mass: 10,000 x 0.9593 = 9,593 kilograms (29.5 degree density, from PPAC)
• Residual line: 9,593 x 3.127 = 29,997 kilograms of CO2
• Diesel per litre figure instead: 10,000 x 2.645 = 26,450 kilograms
• Shortfall: 29,997 minus 26,450 = 3,547 kilograms, 11.8%

Use the density and temperature on your invoice or certificate. The 10,000 litres is an example quantity.

What Senseible does here

Senseible reads litres and tonnes of furnace oil and LDO from invoices. Choosing the IPCC line is your call, so keep the certificate with the invoice.

• Factors for light diesel oil and heavy stock invoices
• Furnace oil litres to kilograms
• LDO tonne to litres
• Bulk diesel invoice in kilolitres at 15 C
• Furnace oil to piped natural gas switch

Sources: IPCC 2006 Guidelines, Volume 2 Chapter 1, Table 1.1 (fuel definitions) and Table 1.2, IPCC 2006 Guidelines, Volume 2 Chapter 2, Table 2.3, PPAC Ready Reckoner FY 2025-26, Table 9.2 (weight to volume conversion)

Last reviewed 2026-11-05. The 44% blend point assumes ideal volume mixing and uses PPAC's densities at 29.5 degrees Celsius; it is our estimate, not an IPCC or PPAC figure. Use the blend's own certificate when you have it. Senseible's standard furnace oil factor is 2.97 kilograms of CO2 per litre at an assumed 0.95 kilograms a litre; PPAC's 29.5 degree density gives about 3.00, so the shortfall is about 11% to 12% depending on the density used.