What methane does the Intergovernmental Panel on Climate Change give per kilometre for compressed natural gas and liquefied natural gas buses and trucks, and how does that compare with its per-energy default?

The Intergovernmental Panel on Climate Change (IPCC) 2006 gives 7,715 milligrams of methane (CH4) per kilometre for a compressed natural gas (CNG) bus and 5,983 for a heavy CNG vehicle. For an example bus running 100,000 kilometres a year that is about five times the methane from the per-energy default of 92 kilograms per terajoule (TJ).

Table 3.2.4: alternative fuel vehicles, milligrams per kilometre

• Light duty vehicles, nitrous oxide (N2O) then CH4: methanol 39 and 9; CNG 27 to 70 and 215 to 725; liquefied petroleum gas (LPG) 5 and 24; ethanol 12 to 47 and 27 to 45.
• Heavy duty vehicles: methanol 135 and 401; CNG 185 and 5,983; liquefied natural gas (LNG) 274 and 4,261; LPG 93 and 67; ethanol 191 and 1,227.
• Buses: methanol 135 and 401; CNG 101 and 7,715; ethanol 226 and 1,292.
• The table's sources are United States Environmental Protection Agency data and a Brazilian study, so these are not Indian engines.

The per-energy default it sits beside

Table 3.2.2 gives natural gas road vehicles 92 kilograms of CH4 and 3 of N2O per TJ, and LPG 62 and 0.2. The table notes say these were converted from per-kilometre data by assuming 9 kilometres per litre of petrol-equivalent for natural gas vehicles. That is the fuel use of a car. A bus or heavy truck burns several times more energy per kilometre, so a per-energy factor built on a car's fuel economy does not fit it. Part of the gap is also different data: the natural gas default in Table 3.2.2 comes from a 2003 European study done in the Netherlands, while Table 3.2.4 uses United States and Brazilian data. This explanation is our reading; the guide does not compare the two tables.

What the guide asks of you

• It says default factors that do not specify vehicle technology are highly uncertain, and that technology-specific factors should be used if CH4 and N2O from mobile sources are a key category. That wording is written for national inventories.
• It says anyone using the Table 3.2.2 defaults should note the assumed fuel economy values and the representative vehicle categories behind them.
• It warns that alternative fuel factors tend to have a high degree of uncertainty, given the wide range of engine technologies and the small samples behind them.

How to use them

Per kilometre needs your own distance travelled by vehicle type, from trip logs or odometer readings. Per energy needs only the fuel bills. If a bus or truck is a large part of your Scope 1, calculate both and disclose which one you report and why. The example shows how far apart they can be.

One CNG bus, 100,000 kilometres a year (example quantities)

• Assumed fuel economy 3.0 kilometres per kilogram of CNG: 100,000 / 3.0 = 33,333 kilograms of CNG
• Carbon dioxide (CO2): 33,333 x 2.69 = 89,667 kilograms, which is 89,667 / 56,100 = 1.598 TJ
• Per energy: CH4 1.598 x 92 = 147 kilograms; N2O 1.598 x 3 = 4.8 kilograms
• Per kilometre, CNG bus: CH4 100,000 x 7,715 milligrams = 771.5 kilograms; N2O 100,000 x 101 milligrams = 10.1 kilograms
• At example global warming potentials (GWP) of 28 and 265, in kilograms of carbon dioxide equivalent: per energy 4,117 + 1,271 = 5,388, which is 6.0 percent of the CO2; per kilometre 21,602 + 2,677 = 24,279, which is 27.1 percent
• The per-kilometre methane is 771.5 / 147 = 5.2 times the per-energy figure

The 100,000 kilometres, the 3.0 kilometres per kilogram and the GWP values are example numbers. 2.69 kilograms of CO2 per kilogram of CNG is the factor used on the CNG three-wheeler page.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so CNG or LNG bought shows up once uploaded. Kilometres run by each vehicle are not on a fuel bill, so keep trip logs if you use the per-kilometre route.

• CNG three-wheeler cargo vehicles
• Electric or LNG truck against diesel
• Fleet fuel card statements as evidence
• Free calculators

Sources: IPCC 2006 Guidelines, Volume 2 chapter 3: Mobile Combustion (Tables 3.2.2 and 3.2.4)

Last reviewed 2026-11-05. Factors are 2006 IPCC defaults from United States and Brazilian data. The two routes can differ by a factor of five or more, so ask your verifier which one they accept for a CNG or LNG fleet.