The two systems at a glance
| IMO DCS | EU MRV | |
|---|---|---|
| Applies to | Ships ≥ 5,000 GT on international voyages | Ships ≥ 5,000 GT calling at any EU/EEA port |
| Reporting unit | Annual aggregate | Per-voyage + annual |
| Key data | Fuel per type, distance, hours underway | Fuel per type, distance, hours, voyage start/end ports, cargo, time at sea vs at berth |
| Scope weighting | No (global) | Yes - 100 % / 50 % / 0 % by voyage type |
| Governing framework | MARPOL Annex VI Reg 22A + MEPC.282(70) | Regulation (EU) 2015/757 (as amended) |
| Submitted to | Flag state → IMO GISIS | Verifier → THETIS-MRV (EMSA) |
| Public? | No (aggregated published) | Yes - per-ship emission intensity |
| Output | SoC + aggregate index | Document of Compliance + EU Emission Report |
| Feeds | CII rating | CII (for IMO ships), EU ETS, FuelEU Maritime |
Monitoring plan: the one document that drives both
Both regimes require a verifier-approved monitoring plan:
- IMO DCS plan = SEEMP Part II (MEPC.282(70)).
- EU MRV plan = Monitoring Plan per Article 6 of 2015/757.
Content largely overlaps:
- Ship identification, ownership, fuel types usable.
- Fuel flow measurement method - BDN + tank sounding, flowmeter, or direct CO₂ measurement.
- Uncertainty analysis per method.
- Data gap procedures.
- Verifier identity.
Most operators maintain one combined plan document with a small annex that lists the MRV-only fields (per-voyage granularity tables, cargo-carried definition for EEOI-style metrics).
Measurement methods
Both regimes accept the same four methods, in priority order:
- BDN + periodic fuel-tank sounding - mass-balance over the reporting period. Default fallback. Our BDN/ROB calculator automates this.
- Bunker fuel tank monitoring - more frequent tank-level logging for higher granularity.
- Flow meters - Coriolis mass-flow meters on the ME/AE fuel lines. Highest accuracy.
- Direct CO₂ emission measurement - continuous emission monitoring system (CEMS) on exhaust. Rare; only retrofit on research vessels and some LNG carriers.
Pick one method per fuel line; changes mid-year require a re-validation from the verifier.
The per-voyage twist
DCS doesn’t care which voyage the fuel was burned on. MRV does - it needs:
- Port of departure + port of arrival + date/times
- Fuel consumed at sea
- Fuel consumed at berth
- Distance travelled
- Cargo carried (for passenger: pax numbers; for cargo: mass or volume)
- Time at sea and time at berth
This per-voyage detail is what enables MRV to be re-used for EU ETS scope weighting (50/100 %) and FuelEU Maritime (which also distinguishes EU-to-EU vs extra-EU).
Cf factors
Both regimes use IMO MEPC.364(79) Cf factors to convert fuel mass to CO₂ mass. This avoids two different emission accounting conventions. Example values:
| Fuel | Cf (t CO₂ / t fuel) |
|---|---|
| HFO, VLSFO, ULSFO | 3.114 |
| MGO, MDO | 3.206 |
| LNG (Otto DF, slip-corrected) | 2.750 |
| Methanol | 1.375 |
| Ammonia | 0.000 |
| Hydrogen | 0.000 |
FuelEU Maritime adds WtW emission factors (upstream + methane slip + N₂O); those live in Annex II of Regulation 2023/1805, not in MEPC.364. Different regime, different denominator.
Verification
Both regimes use accredited third-party verifiers:
- DCS: verifier accredited by the flag administration; many use a class society (DNV, ABS, LR, BV, NK, RINA) that does the SoC at the same time.
- MRV: verifier accredited under EU Regulation 2015/757 Implementing Regulation 2016/2072 (typically, a subset of the same class societies). EMSA publishes the list.
Many operators use the same verifier for both - the monitoring plan audit is duplicated otherwise.
Timeline each year
| Date | DCS | MRV |
|---|---|---|
| 31 Jan | - | Emissions report due to verifier |
| 28 Feb | Verified report due | - |
| 31 Mar | Flag state notifies IMO | Verified report + DoC due to THETIS-MRV |
| 30 Apr | - | Pool registration deadline (FuelEU) |
| 30 Jun | - | Report made public on THETIS |
| 30 Sep | - | EUA surrender deadline (ETS) |
The two systems share the Q1 data-prep workload but diverge on downstream obligations. Plan for both simultaneously.
Reporting pitfalls
- Port-state inspection loss. If voyage-boundary timestamps aren’t logged (e.g. AIS-only with gaps), MRV’s per-voyage aggregation fails verification. Always log departure/arrival manually in the log book.
- Bunker loading vs consumption date. DCS cares about consumption; MRV cares about both. A bunker in December used in January straddles both years - document the split.
- Debunkering and fuel transfers. Both regimes require explicit deduction from the mass balance. Omitting a bunker-to-bunker transfer shows up as ghost fuel.
- Scope boundary. For MRV, a voyage that touches an EU port at 50 % scope needs the full voyage reported (EU expects to see the “other half” even though it’s counted at 50 %). Getting this wrong skews the ETS liability.
- LNG methane slip. MEPC.364 Cf for LNG already embeds a slip factor; don’t add it twice. FuelEU separately applies a slip factor to the WtW intensity.
Why a unified data architecture matters
One modern setup:
- On-board: FMS + AMS (alarm monitoring) logs fuel flow, engine load, voyage events every 15 minutes.
- Shore: Data lake aggregates logs + BDNs + voyage orders.
- Reporting module: Produces DCS aggregate, MRV per-voyage, ETS covered-CO₂, FuelEU WtW - all from the same source.
- Verifier portal: Verifier reads the same data set for DCS and MRV, cuts audit time in half.
Operators who treat DCS and MRV as separate workflows spend 2–3× more on compliance staff and still end up with mismatched numbers at the verifier stage.
How to compute your numbers
Try our IMO DCS Annual Report calculator for the MARPOL 22A aggregate. Use EU MRV Emissions for the per-voyage rollup (with scope weighting). BDN / ROB Reconciliation handles the mass-balance if you’re not on a flow meter. The results feed directly into the CII Attained, EU ETS Liability, and FuelEU GHG Intensity calculators.