Vessels calling at Zhoushan, China's largest bunkering hub, now wait one to two weeks to refuel — up from a normal one to two days — as fuel oil supplies tighten in the fallout from the US-Iran war.

People familiar with the matter, who asked not to be identified because they are not authorized to speak to media, confirmed the extended waiting times at the port south of Shanghai. Ningbo Zhoushan Port did not immediately respond to a request for comment.

Two forces are driving the squeeze. Crude import constraints linked to the Middle East conflict have tightened feedstock availability. At the same time, Chinese refiners have shifted slate toward gasoline and diesel to capture stronger margins, cutting residual fuel oil output and shrinking bunker fuel supply.

The numbers show the strain. China's state-owned refiners produced 1.12 million tons of low-sulfur fuel oil in August, down 13% from July, according to energy data provider JLC. Spot prices for very low-sulfur fuel oil at Zhoushan on Tuesday sat near their highest level since March — the early days of the Iran war — per bunker data provider ClearLynx LLC. Zhoushan VLSFO now commands a premium of more than 25% over Singapore, its rival Asian bunkering hub.

For shipowners and operators, the commercial calculus is already shifting. A one-to-two-week wait for stems at China's top hub erodes voyage economics and pushes carriers toward Singapore, where fuel is markedly cheaper and turnaround faster. Forwarders and operators routing Asia-bound tonnage through Chinese ports face higher overall fuel spend or schedule risk if they persist with Zhoushan stem plans.

The timing complicates matters further. China begins a week-long national holiday on Thursday, and bunkering activity across several Chinese ports is expected to slow over the period.

Relief is in sight, though modest. Tightness in the fuel oil market should ease in early October, driven primarily by a seasonal demand pullback rather than a supply recovery.

The disruption touches a strategic nerve for Beijing. China has long worked to build Zhoushan into a regional bunkering hub to rival Singapore, using a fuel oil tax rebate to offer competitive prices, attract Asia-bound commercial fleets and encourage domestic refiners to raise low-sulfur fuel oil output. The city-state remains the clear leader in ship refueling, and a two-week queue plus a 25% price premium at Zhoushan hands Singapore an open goal at the very moment China's hub ambitions face their stiffest test. If refiners keep prioritizing gasoline and diesel margins, Zhoushan's competitiveness — and the traffic Beijing has courted with tax incentives — could drift back toward Singapore until low-sulfur fuel oil output recovers.