Which methane factor should petrol-driven off-road machinery use in the Intergovernmental Panel on Climate Change guide: two-stroke or four-stroke?

In the Intergovernmental Panel on Climate Change (IPCC) 2006 off-road table, a two-stroke petrol engine in industry has a methane (CH4) default of 130 kilograms per terajoule (TJ), against 50 for a four-stroke. Nitrous oxide (N2O) runs the other way, 0.4 against 2.

The petrol rows of the off-road table

• Four-stroke, kilograms per TJ of CH4 then N2O: agriculture 80 and 2, industry 50 and 2, household 120 and 2. The table prints no figures for forestry on four-stroke.
• Two-stroke, CH4 then N2O: agriculture 140 and 0.4, forestry 170 and 0.4, industry 130 and 0.4, household 180 and 0.4.
• Carbon dioxide (CO2) is 69,300 kilograms per TJ in every row, with a range of 67,500 to 73,000.
• The CH4 ranges are wide: 20 to 125 for four-stroke industry and 52 to 325 for two-stroke industry. The table note says the CH4 figures include "diurnal, soak and running losses"; our gloss is that this covers fuel evaporation as well as exhaust.

Which row is yours

The table has no row for a machine type. It has rows for the sector the machine works in and for the engine stroke. A chainsaw on a plantation is a forestry two-stroke. A brush cutter on a farm is an agriculture two-stroke. Our reading is that a petrol pump or loader inside a factory uses the industry row; the guide does not name examples.

The table note says that where fuel use by sector is not split, the defaults may be set by national circumstances, for example how common a sector is or by weighting by activity. Our reading: the same logic applies if you cannot tell two-stroke fuel from four-stroke fuel on your bills, so write down how you weighted the split.

What the numbers mean for a petrol bill

Our reading of the stroke split, at the global warming potentials in the example: methane is the larger part in both cases, and nitrous oxide is the larger share for four-stroke (53 of 193 kilograms of carbon dioxide equivalent) than for two-stroke (10.6 of 374.6). Together the two gases add about 2.8 percent to the CO2 for a four-stroke engine in industry and about 5.4 percent for a two-stroke engine. These are small shares, so the choice matters most for a large fleet of hand tools.

Diesel machinery is different. The diesel rows in the same table give 4.15 kilograms of CH4 and 28.6 of N2O per TJ for every sector.

The note on catalysts

The table note says off-road vehicles in general do not have emission control catalysts, with possible exceptions in urban areas, such as ground support equipment at airports and harbours. Working catalysts turn nitrogen oxides into N2O and methane into CO2, and one exposure to high-sulphur or leaded fuel permanently damages them. If your machine has a catalyst and has been run on high-sulphur or leaded fuel, the guide says to consider that damage when adjusting the factors.

3,000 litres of petrol in industry (example quantities)

• CO2: 3,000 x 2.31 = 6,930 kilograms, which is 6,930 / 69,300 = 0.1 TJ
• Four-stroke: CH4 0.1 x 50 = 5 kilograms; N2O 0.1 x 2 = 0.2 kilograms
• Two-stroke: CH4 0.1 x 130 = 13 kilograms; N2O 0.1 x 0.4 = 0.04 kilograms
• At example global warming potentials (GWP) of 28 for CH4 and 265 for N2O, in kilograms of CO2 equivalent: four-stroke 140 + 53 = 193; two-stroke 364 + 10.6 = 374.6
• Against the 6,930 kilograms of CO2: four-stroke 2.8 percent, two-stroke 5.4 percent

The 3,000 litres and both GWP values are example numbers. 2.31 kilograms of CO2 per litre of petrol is the factor used elsewhere on this site.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the petrol bought shows up once uploaded. Bills do not say which machine burnt it or whether it was a two-stroke or four-stroke engine, so keep a note of that split.

• Diesel machinery on a farm
• Why the same fuel has different methane by table
• Methane and nitrous oxide from diesel
• Free calculators

Sources: IPCC 2006 Guidelines, Volume 2 chapter 3: Mobile Combustion (Table 3.3.1)

Last reviewed 2026-11-05. Factors are the 2006 IPCC Tier 1 defaults, which the guide says are based on European off-road machinery. Confirm with your verifier which sector row you use for each machine.