The global shipping industry is under increasing pressure to use cleaner fuel to reduce both carbon and sulphur dioxide emissions and other pollutants and meet broader green targets.

Hundreds of tankers that are transporting sanctioned oil are posing a challenge since they are hard to track because of their opaque ownership and use of non-Western insurance and other marine services, and they have little incentive to follow cleaner shipping standards.

"You're seeing greater numbers of ships that have found ways to circumvent sanctions by operating outside Western jurisdiction," said Michelle Wiese Bockmann, principal analyst with maritime data group Lloyd's List Intelligence.

"The dark fleet has gone on steroids. And the deceptive shipping practices that they're engaging in are getting more and more complex and sophisticated."

Those include dangerous ship-to-ship transfers of oil in international waters to avoid port state control scrutiny, falsifying ship identification numbers, tankers sending false information about their position, and the use of flag registries with lower standards of technical oversight and expertise, Bockmann said.

Lloyd's List Intelligence estimates the shadow fleet had grown to around 630 tankers from 530 a year ago, to make up 14.5% of the overall global tanker fleet.

Some industry estimates put the number even higher, at over 800 tankers.

The numbers mark further rapid expansion following Moscow's invasion of Ukraine in 2022 and Western curbs on Russian energy exports, which has led to ships being hit with sanctions.

Before the war, the shadow tanker fleet totalled around 280-300 vessels, according to Lloyd's List Intelligence.

Such growth has raised concerns about its environmental impact as well as safety and the effectiveness of sanctions, including a Western ban on shipment and trading of Russian oil priced above a $60 per barrel limit.

Under the so-called IMO 2020 convention adopted by the United Nations' International Maritime Organization (IMO), ships have to switch to low sulphur fuel from the higher sulphur fuel diesel the industry has used for decades.

NO 'SCRUBBERS'

Enforcement of these regulations designed to lower emissions is up to IMO member countries, which can levy fines or detain ships for non-compliance. In April, the IMO called on its members to increase inspections on vessels deemed to be shadow ships and toughen fines for any irregularities.

The IMO rules say ships can only burn high sulphur fuel if they have exhaust gas cleaning systems, known as scrubbers.

Shadow fleet tankers, however, can run on higher sulphur diesel - that is estimated to cost 20% less than the greener fuel - without checks unless they are stopped at ports enforcing the regulations, people familiar with the matter said.

"A lot of shadow vessels have no scrubbers but they buy high sulphur fuel oil when they are in Russia," one industry source said. "So, they are breaching the IMO's sulphur limit."

It is difficult to gauge the extent of non-compliance with IMO 2020 across the shadow fleet, but there has been a rise in cases of ships detained because of sulphur-related breaches.

Port authorities in Europe and Asia detained at least 10 ships in the first five months of 2024 in connection with the convention, up from six in the same period last year and five for the whole of 2022, according to Reuters analysis based on data from port enforcement authorities. Of the 10 tankers detained, nine had made previous calls to Russia.

RUSSIAN, IRANIAN FUEL SUPPLIES

Russia and its partners in the Eurasian Economic Union, which includes Kazakhstan, Kyrgyzstan, Armenia and Belarus agreed in December they would continue using high sulphur fuel until the end of 2026.

This means that ships can still get high sulphur fuel at ports servicing those countries, people involved in the fuel shipping trade say.

Iran, another producer of high sulphur fuel, has supplied ships in the Middle East Gulf, the sources say.

In one such operation, the Casinova tanker loaded such fuel at Iran’s Bandar Imam Khomeini port in recent months, said Claire Jungman, chief of staff at U.S. advocacy group United Against Nuclear Iran, which tracks Iran-related tanker traffic via satellite data. The Casinova later transferred some of the fuel onto smaller ships waiting around the Basra Anchorage in southern Iraq, Jungman said.

The vessel's Liberia based owner Le Monde Marine Services could not be reached for comment.

Casinova's ship insurer West P&I said it was in the process of cancelling the vessel's coverage after Reuters requested comment.

Ship certifier ABS, which has provided safety cover for the Casinova, was investigating its activity, a spokesperson for the U.S.-headquartered company said.

"ABS treats every allegation and the subject of sanctions very seriously," the spokesperson said. "We remain committed to compliance with U.S. and UN sanctions regimes and all other applicable laws."