Marine and Aviation Fuel (Own Operations)
A company that owns a ship or an aircraft burns fuel the same way a company that owns a truck does — and the carbon accounting is, at its core, the same fuel-based calculation. Yet marine and aviation own-operations emissions are among the most frequently mis-scoped lines in any inventory.
The fuel is Scope 1. Almost everything that confuses reporters about it is not.
Fuel burned in an organisation’s own or controlled ships and aircraft is Scope 1 mobile combustion: fuel quantity × a fuel-specific emission factor. Upstream fuel supply (well-to-tank) is Scope 3, and aviation radiative forcing is a separate non-Kyoto memo item — never inside the Scope 1 figure.
Marine and aviation fuel combustion in an organisation’s own fleet is conceptually simple — it is fuel-based mobile combustion, the same arithmetic as a diesel truck — but it carries three complications that road fuel does not: fuel is often metered in tonnes rather than litres, the upstream supply chain is material and reported separately, and aviation has a non-CO₂ warming effect that sits outside the Kyoto greenhouse-gas inventory. This page separates the Scope 1 fuel calculation from everything that surrounds it, sets out the fuel factors and measurement bases, and resolves the radiative-forcing question that derails more aviation inventories than any other.
Why This Is Scope 1, and What Isn’t
The boundary rule is the one from the GHG Protocol Corporate Standard: fuel combusted in assets the organisation owns or controls is Scope 1. A company-owned vessel or aircraft is such an asset, so the fuel it burns — regardless of where in the world the combustion happens — is the reporting organisation’s direct emission.
This is mobile combustion, the same category as the road fleet, distinguished only by the fuels involved and the measurement units. What it is not:
| Activity | Scope | Why |
|---|---|---|
| Fuel burned in an owned/controlled ship or aircraft | Scope 1 | Direct combustion in a controlled asset — mobile combustion |
| Upstream supply of that fuel (extraction, refining, transport) | Scope 3 Cat 3 | Well-to-tank — fuel- and energy-related, not in any other scope |
| Aviation non-CO₂ radiative forcing (contrails, NOx) | Memo item (non-Kyoto) | Outside the GHG inventory’s Kyoto gas basis — reported separately, never in Scope 1 |
| Chartered vessel/aircraft the organisation does not control | Scope 3 Cat 4/6/9 | No operational control → upstream or downstream transport, or business travel |
| Employee commercial flights | Scope 3 Cat 6 | Business travel on aircraft the organisation does not operate |
The same litre of jet fuel can be Scope 1 (your own aircraft), Scope 3 Category 6 (an employee on a commercial flight), or Scope 3 Category 4 (a freight charter you pay for). This methodology covers only the first case — fuel burned in assets you own or operationally control. If you do not control the aircraft or vessel, the emission is someone else’s Scope 1 and your Scope 3, calculated on a different basis. Fix the control boundary before selecting any factor.
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The Three Emission Layers
A single fuel burn generates up to three reportable quantities, in three different places in the inventory. Keeping them separate is the discipline this topic demands.
The terms well-to-tank and tank-to-wake are the marine and aviation equivalents of well-to-tank and tank-to-wheel. The combustion layer — tank-to-wake — is the Scope 1 figure this methodology calculates. The upstream layer is the well-to-tank Scope 3 methodology, calculated with a separate set of upstream factors. The radiative-forcing layer applies to aviation only and is addressed in §6.
The fuel emission factors used for the Scope 1 calculation cover direct combustion — they do not include the upstream well-to-tank component, and for aviation they do not include radiative forcing. This is correct and deliberate. Adding a well-to-tank or radiative-forcing uplift into the Scope 1 line double-counts against Scope 3 or imports a non-Kyoto effect into the Kyoto inventory. The Scope 1 figure is the clean combustion number; the other layers are reported in their own places.
The Calculation
The core calculation is fuel quantity multiplied by a combustion emission factor, summed across every fuel and every asset.
The factor bundles the three combustion gases — CO₂, CH₄, and N₂O — into a single CO₂e value at the AR5 GWP-100 basis that the DEFRA dataset uses by convention. Where a gas-by-gas split is required (for example, to convert to an AR6 basis), the per-gas components are available behind the aggregate factor, but the headline calculation uses the bundled CO₂e figure.
The well-to-tank Scope 3 companion uses the identical structure with the upstream factor:
Marine and Aviation Fuels and Factors
The fuels diverge from road transport. Marine operations run on distillate and residual fuel oils; aviation runs on kerosene-grade turbine fuel or, for piston aircraft, aviation spirit. The combustion factors below render live from the platform’s mobile-combustion dataset (DEFRA 2026, AR5 GWP-100, per litre).
Marine fuels Marine
| Fuel | Used for | Factor (kg CO₂e/litre) |
|---|---|---|
| Marine gas oil (MGO) | Distillate — manoeuvring, auxiliary engines, smaller vessels | 2.77139 |
| Marine fuel oil (residual) | Heavy residual — main propulsion at sea on larger vessels | 3.10202 |
| Fuel oil (residual) | General residual fuel oil | 3.17492 |
| Gas oil (red diesel) | Distillate for inland and smaller marine engines | 2.75541 |
Aviation fuels Aviation
| Fuel | Used for | Factor (kg CO₂e/litre) |
|---|---|---|
| Aviation turbine fuel (Jet A / A-1) | Kerosene — turbine and turboprop aircraft | 2.54269 |
| Aviation spirit (avgas) | Gasoline — piston-engine aircraft | 2.33116 |
The residual fuels carry the highest carbon intensity per litre — heavier hydrocarbons, more carbon per unit volume — which is why a vessel running heavy fuel oil for main propulsion dominates the marine footprint even when distillate volumes are similar. Each factor is the tank-to-wake combustion value only; the well-to-tank companion is held separately and reported in Scope 3.
Fuel Measurement Basis: Litres, Tonnes, Energy
Road fuel is almost always metered in litres. Marine bunkers are usually metered in tonnes, and aviation fuel may be recorded in litres, kilograms, or energy. The factor basis must match the activity-data basis, or the result is wrong by the density ratio.
| Basis | Typical use | Factor key suffix |
|---|---|---|
| Per litre | Aviation fuel uplift records; smaller marine vessels | .per_litre |
| Per tonne | Marine bunker delivery notes (the dominant marine basis) | .per_tonne |
| Per kWh (net CV) | Energy-basis consumption already converted to kWh | .per_kwh_net_cv |
| Per kWh (gross CV) | Energy-basis consumption on gross calorific value | .per_kwh_gross_cv |
If the bunker delivery note is in tonnes, use the per-tonne factor directly. Converting tonnes to litres with a generic density introduces error, because residual fuel oil density varies with grade and temperature. The platform holds per-litre, per-tonne, and two energy bases for every marine and aviation fuel — select the one that matches your meter, rather than converting the activity data to fit a single factor.
Aviation Radiative Forcing
Aircraft warm the climate by more than their CO₂ alone. Contrails, contrail-induced cirrus, and high-altitude NOx emissions add a warming effect — radiative forcing — that is real but sits outside the Kyoto greenhouse-gas basis on which corporate inventories are built. The treatment is precise and frequently mishandled.
The Scope 1 combustion factor is the Kyoto-gas CO₂e of burning the fuel — CO₂, CH₄, and N₂O. Radiative forcing is a non-CO₂, non-Kyoto effect. It is reported, where reported at all, as a separate memo item alongside the inventory, never folded into the Scope 1 line. Folding a radiative-forcing multiplier into Scope 1 mixes a non-Kyoto effect into a Kyoto inventory and breaks comparability with every other emission in the footprint.
The radiative-forcing multiplier on the platform appears only in the passenger air-travel dataset, as explicit with_rf and without_rf variants for Scope 3 Category 6 business travel — where convention applies an uplift to the passenger-kilometre factor. Own-operations fuel-based combustion carries no radiative-forcing field: the combustion factor is the combustion factor. An organisation that wishes to disclose the full climate impact of its own aircraft does so as a clearly-labelled supplementary figure, stating the multiplier and its source, outside the Scope 1 total.
Radiative-forcing science carries genuine uncertainty, and the multiplier used varies by source. Any supplementary radiative-forcing disclosure should state the multiplier applied, cite its source, and present it separately from the Kyoto-gas Scope 1 figure — so a reader can see both the audited combustion number and the wider climate estimate without the two being conflated.
Worked Example — A Marine and Aviation Operator
Fixed audit record at the snapshot date of this methodology revision. An organisation operates one owned vessel and one owned aircraft. The marine fuel is taken from bunker delivery notes and therefore metered in tonnes — so the per-tonne combustion factors apply directly, with no litre conversion. The aviation fuel comes from litre-based uplift records. Factors are DEFRA 2026 combustion values; well-to-tank figures are illustrative upstream companions, shown separately in Scope 3. Substitute your own metered fuel quantities and the current published factors.
The marine fuel oil line alone — 13,249.96 tCO₂e — is the single largest source, a direct consequence of residual fuel’s high intensity and the tonnage burned in main propulsion. Because the marine fuel was taken straight from tonne-denominated bunker notes and matched to the per-tonne factor, no density conversion was needed — and the heavy fuel oil, not the distillate, is clearly where decarbonisation effort concentrates. An aggregated “marine fuel” line would have hidden that.
Activity-Data Hierarchy
The Scope 1 calculation is only as good as the fuel-quantity data behind it. The data hierarchy, best to worst:
- Metered bunker / uplift records. Bunker delivery notes for marine, fuel uplift records for aviation — the primary, auditable source. Preferred wherever available.
- Fuel purchase records. Invoiced fuel quantities, reconciled to consumption with opening and closing tank levels.
- Voyage / flight-hour estimates. Where metered fuel is unavailable, estimated from operating hours and a fuel-burn rate — acceptable as a gap-fill, flagged as estimated.
- Distance-based estimates. The weakest basis — fuel inferred from distance and a vessel/aircraft-class burn rate. A last resort, and a signal to improve metering.
For company aircraft, fuel-based combustion is more accurate than the distance-based passenger-kilometre method used for commercial business travel — because the organisation has the actual fuel uplift, not an averaged seat-kilometre factor. Use the fuel directly whenever the records exist.
Edge Cases and Error Traps
| Error | What happens | How to avoid |
|---|---|---|
| Folding radiative forcing into Scope 1 | An RF multiplier applied to the aviation combustion factor inflates Scope 1 with a non-Kyoto effect and breaks comparability. | Keep Scope 1 to combustion CO₂e. Report any RF figure as a separate, labelled memo item. |
| Adding well-to-tank into the Scope 1 factor | Using a well-to-wake factor for Scope 1 double-counts the upstream supply that belongs in Scope 3 Category 3. | Use the tank-to-wake combustion factor for Scope 1; report well-to-tank separately in Scope 3. |
| Tonne / litre basis mismatch | Applying a per-litre factor to a tonne-metered bunker quantity (or vice versa) — wrong by the fuel density ratio. | Match the factor basis to the meter. Use the per-tonne factor for tonne-metered bunkers directly. |
| Mis-scoping a chartered asset | Booking fuel from a vessel or aircraft the organisation does not control as its own Scope 1. | Confirm operational control first. No control → Scope 3 Category 4, 6, or 9, on a different basis. |
| Aggregating distillate and residual marine fuel | A single “marine fuel” line hides that residual fuel oil drives most of the footprint, obscuring the abatement priority. | Account each fuel grade separately at its own factor. |
| Double-counting employee flights on company aircraft | Counting a flight on the company’s own aircraft as both Scope 1 fuel and Scope 3 Cat 6 business travel. | Own-aircraft fuel is Scope 1 only. Scope 3 Cat 6 is for commercial flights the organisation does not operate. |
Governance and Verification
Marine and aviation own-operations fuel is audited on four points:
- Control boundary. The verifier confirms each vessel and aircraft is owned or operationally controlled, and that chartered or commercial-travel fuel is excluded from Scope 1.
- Activity-data provenance. Fuel quantities trace to bunker delivery notes or uplift records, with the measurement basis (litres or tonnes) documented and matched to the factor.
- Layer separation. The Scope 1 figure is combustion-only; well-to-tank sits in Scope 3 Category 3; any radiative-forcing figure is a separate memo item. No layer is folded into another.
- Factor basis. The fuel factor, its source (DEFRA or national dataset), and its GWP basis (AR5 for DEFRA) are documented per the ISO 14064-1 transparency requirement.
The governing references are the GHG Protocol Corporate Standard for the control boundary and Scope 1 definition, the GHG Protocol Scope 3 Standard for the well-to-tank companion, and DEFRA (or the relevant national dataset) for the combustion factors.
What the Calculator Handles vs What You Decide
The calculator handles
Per-fuel and per-asset combustion totals, basis conversion across litres/tonnes/energy, the parallel well-to-tank Scope 3 companion, the Scope 1 aggregate, and an optional separately-labelled radiative-forcing memo figure for aviation.
You decide before using it
The operational-control boundary for every vessel and aircraft, the activity-data basis (metered vs estimated), the measurement unit that matches your records, and whether to disclose a supplementary radiative-forcing figure and on what multiplier.
Ready to compute your marine and aviation fuel emissions? Open the Marine & Aviation Fuel Calculator →
Frequently Asked Questions
Scope 1, provided the organisation owns or operationally controls the vessel or aircraft. It is mobile combustion — the same category as the road fleet — calculated as fuel quantity multiplied by a combustion emission factor, wherever in the world the combustion occurs. If the asset is chartered or otherwise outside the organisation’s control, the fuel is someone else’s Scope 1 and the organisation reports it in Scope 3 instead, on a different basis. The control boundary decides the scope, not the type of fuel.
No. Radiative forcing — the additional warming from contrails and high-altitude NOx — is a non-CO₂, non-Kyoto effect that sits outside the greenhouse-gas basis on which the inventory is built. The Scope 1 combustion factor covers only the Kyoto gases (CO₂, CH₄, N₂O). Any radiative-forcing figure is reported as a separate, clearly-labelled memo item alongside the inventory, stating the multiplier and its source — never folded into the Scope 1 total, which would mix a non-Kyoto effect into a Kyoto inventory and break comparability.
Use the per-tonne factor, not the per-litre one. The platform holds per-litre, per-tonne, and two energy bases for every marine and aviation fuel, so select the basis that matches your meter rather than converting the activity data. Converting tonnes to litres with a generic density introduces error, because residual fuel oil density varies with grade and temperature. Matching the factor basis to the measurement basis is the single most reliable way to avoid a density-ratio error in marine accounting.
No. The Scope 1 factor is the tank-to-wake combustion value only — the direct emissions from burning the fuel. The upstream supply chain (extraction, refining, distribution) is the well-to-tank component, reported separately in Scope 3 Category 3 using its own upstream factor. Using a well-to-wake factor for Scope 1 would double-count the upstream supply that belongs in Scope 3. Keep the two layers in their own places: combustion in Scope 1, upstream supply in Scope 3.
Company-aircraft fuel is Scope 1 mobile combustion, calculated from actual fuel uplift. Employee flights on commercial airlines are Scope 3 Category 6 business travel, calculated from a distance-based passenger-kilometre factor because the organisation does not operate the aircraft. The fuel-based own-operations method is more accurate, since it uses real fuel data rather than an averaged seat-kilometre factor. Never count a flight on the company’s own aircraft as both — own-aircraft fuel is Scope 1 only.
The residual fuel oils carry the highest per-litre combustion factor, above the distillates such as marine gas oil. Residual fuels are heavier hydrocarbons with more carbon per unit volume, so a vessel running heavy fuel oil for main propulsion typically dominates its marine footprint even when distillate volumes are comparable. Accounting each fuel grade separately, rather than aggregating to a single marine-fuel line, reveals that the residual fuel is where decarbonisation effort concentrates.