Insights · Compliance · IMO 2020
On 1 January 2020 the world's merchant fleet had to switch to far cleaner fuel almost overnight. The IMO 2020 sulphur cap, set under MARPOL Annex VI, slashed the allowed sulphur in marine fuel sevenfold — and inside Emission Control Areas the limit is tighter still.
For most of the twentieth century, deep-sea ships ran on heavy fuel oil — the thick, cheap residue left at the bottom of the refining barrel, and one of the most sulphur-rich fuels in routine use anywhere. Burning it at sea released sulphur oxides (SOx) that contribute to acid rain and to the fine particulates linked to respiratory and cardiovascular disease near busy coastlines. The IMO 2020 sulphur cap is the regulation that finally brought that to an end on a global scale.
The rule lives in MARPOL Annex VI, the air-pollution annex of the International Convention for the Prevention of Pollution from Ships, administered by the International Maritime Organization. From 1 January 2020, the maximum sulphur content of fuel oil used by ships outside designated control areas fell from 3.50% to 0.50% mass by mass (m/m) — a sevenfold reduction applied to the entire world fleet at the same moment.
Three numbers tell the whole story. There is the old global limit, the current global cap, and the much tighter figure that applies inside an Emission Control Area.
| Where / when | Sulphur limit (m/m) | In force from |
|---|---|---|
| Global — before IMO 2020 | 3.50% | 2012 |
| Global — IMO 2020 cap | 0.50% | 1 Jan 2020 |
| Inside an ECA (SOx) | 0.10% | 1 Jan 2015 |
The 0.10% figure is five times tighter than the 0.50% global cap, which is why operators have to pay close attention to exactly where a ship is sailing. Cross into an ECA and the fuel has to change too — or the exhaust has to be cleaned to the equivalent standard.
An Emission Control Area is a sea region where MARPOL Annex VI imposes stricter emission limits than the global baseline, because of the density of traffic and population around it. ECAs can be designated for sulphur oxides (SOx), nitrogen oxides (NOx), or both. As of 2026 there are five SOx Emission Control Areas, and the list has grown over time.
| SOx Emission Control Area | In force from |
|---|---|
| Baltic Sea | 2006 |
| North Sea | 2007 |
| North American area (US & Canada coasts) | 2012 |
| United States Caribbean Sea area | 2014 |
| Mediterranean Sea | 1 May 2025 |
The Mediterranean Sea is the newest: it became a SOx ECA on 1 May 2025, extending the 0.10% limit across one of the world's busiest cruise and container basins. Annex VI also governs nitrogen oxides through Tier I, II and III standards; the strictest, Tier III, applies to engines on ships built from set dates operating in designated NOx ECAs — for the North American, US Caribbean, Baltic and North Sea NOx areas this catches ships built on or after 1 January 2021.
A ship has two legitimate routes to staying within the cap, and the choice has reshaped the fuel market and the fleet's plumbing alike.
The straightforward route is to buy fuel that already meets the limit — very-low-sulphur fuel oil (VLSFO, at or below 0.50%) for open water, and marine gasoil (MGO, typically at or below 0.10%) for ECAs. Most of the fleet took this path. It needs no hardware, but the cleaner fuel costs more, and switching grades when crossing an ECA boundary has to be logged and managed carefully.
The alternative is to fit an exhaust gas cleaning system — a "scrubber" — which removes sulphur oxides from the exhaust so the ship can keep burning cheaper high-sulphur fuel oil (HSFO) while still meeting an equivalent standard. Open-loop scrubbers wash the exhaust with seawater and discharge the wash-water back to sea, a practice that is now banned or restricted in a number of ports and coastal waters. Closed-loop systems retain the wash-water on board for later disposal ashore. The economics turn on the price gap between HSFO and compliant fuel.
On and after 1 January 2020 the sulphur content of any fuel oil used on board ships shall not exceed 0.50% m/m. MARPOL Annex VI, regulation 14, IMO
Compliance is not left to good faith. Every ship subject to Annex VI carries an International Air Pollution Prevention (IAPP) certificate, and Port State Control inspectors can sample the fuel in the tanks and check the Bunker Delivery Note against what is actually being burned. Since 1 March 2020 a "carriage ban" has gone further still: a ship is prohibited from even carrying non-compliant fuel oil for combustion unless it has a scrubber fitted. That closed the loophole of buying cheap fuel and only switching grades at the last moment.
For anyone screening a vessel, the sulphur regime sits alongside the rest of a ship's regulatory standing. You can look up any of 97,000+ vessels in the Marifest registry to see its type, flag, builder and ownership chain, and read terms like VLSFO, MGO and ECA in the maritime glossary when a certificate or detention record refers to them.
How Marifest uses it
The sulphur cap is one strand of a vessel's compliance picture. Marifest pulls together identity, flag, ownership and screening so the regulatory context around a hull is in one place — including where it trades and which rules bite there.
Each vessel record ties the hull to its flag, builder and ownership chain — the backdrop against which Annex VI obligations like the IMO 2020 cap apply.
Terms such as VLSFO, MGO, scrubber and ECA are defined in the Marifest glossary, so a Bunker Delivery Note or detention notice reads straight.
The live map shows movement against the world's ECAs, the regions where the 0.10% limit replaces the 0.50% global cap.
Sanctions matching against OFAC, EU, UN and UK lists runs next to a vessel's identity, so environmental and trade-compliance flags surface together.