Aframax and Suezmax vessels have become more active on the sensitive route, ship-tracking data show.
Eight such tankers received Iranian crude from supertankers via ship-to-ship (STS) transfers in February, with the majority of them bound for China, according to Kpler data.
That compares with two tankers each in December and January.
The use of smaller vessels in the Iran-China trade, typically dominated by very large crude carriers (VLCC), also known as supertankers, has piqued the interest of shipping firms.
“The shift is likely due to their ability to discharge oil at shallower Chinese berths – such as Dongying – that are increasingly being used to receive Iranian and Russian shipments,” said shipbrokers and analysts.
“Bigger terminals that also handle containers and bulk cargoes have become wary of secondary sanctions,” they said.
A ramping up of US sanctions by the Biden administration and president Donald Trump’s vow to use “maximum pressure” against Tehran have resulted in the blacklisting of dozens of ships in recent months, hitting the more frequently-used VLCCs harder than other vessel classes.
The tougher restrictions on the use of supertankers and wariness from some Chinese ports about handling Iranian oil, has increased the amount of STS transfers at sea and the use of Aframaxes and Suezmaxes.
Strategies to reconfigure supply chains to make sure Iranian oil can still flow to China are evolving in the face of US sanctions on Tehran.
While exports from ports such as Kharg Island were previously reliant on Iranian-owned VLCCs that sailed directly from the Persian Gulf to China, scrutiny and clampdowns have resulted in more ship-to-ship transfers at locations off Malaysia and Fujairah to mask the cargoes’ origins.
Prior to February, almost all STS operations done off Malaysia were carried out between supertankers, Kpler data show.
VLCCs have an oil-carrying capacity of about 2 million barrels, while Suezmax and Aframax ships can move about 1 million and 700,000 barrels, respectively.
Multiple transfers and the use of smaller tankers can add to overall transportation costs.
In February, sanctioned supertanker Lan Jing – previously called Wen Yao – transferred Iranian crude in three separate STS operations to Aframaxes Reston, Brava Lake and Shun Tai off Malaysia, according to Kpler.
The vessels were bound for the ports of Huangdao, Dongying and Zhoushan, respectively.
In the same month, Iranian VLCC Derya discharged its cargo to Suezmax Aventus I and Aframax Viola.
The shipments were bound for Dongjiakou and Dongying.