The current situation

Since the closure of the Strait of Hormuz to most commercial shipping in late February 2026, an estimated 1,550 vessels, carrying approximately 20,000 seafarers, have been unable to transit, or have chosen to remain at anchor in the Arabian Gulf, Gulf of Oman, and approaches. Traffic through the Strait, which normally averages around 138 vessels per day, has fallen to near-zero on most days. The conflict began on 28 February 2026, resulting in vessels being idle for approximately 90 days. Many are expected to remain idle until a navigable resolution to the situation emerges, which cannot be predicted at this time.

For vessel owners and operators responsible for such vessels, there is a need to focus on the technical consequences of extended idle upon fuel quality and what needs to be done in order to protect the vessel, crew and the environment.

Fuel quality deterioration during extended idle

Fuel deterioration in idle vessels is caused by a combination of time, temperature, water ingress, and inactivity. Each mechanism reinforces the others. The Arabian Gulf summer (June–September) is one of the most demanding storage environments in global shipping, with bunker tank temperatures on unshaded anchored vessels regularly reaching 50–55°C.

Biofuel blends

The UAE, principally Fujairah and Jebel Ali, has begun supplying ISCC-certified marine biofuel blends, primarily FAME (UCOME) blended into VLSFO, at concentrations typically ranging from B10 to B30 (10–30% FAME by volume). Vessels that bunkered biofuel blends before going idle face additional degradation risks that do not apply to conventional fuel:

• FAME (UCOME) blends may exhibit reduced storage stability. Although storage life varies, a typical shelf life is often considered to be around 3 to 4 months, after which the risk of oxidation, acid formation and microbial contamination may increase, particularly under elevated ambient temperatures.
• FAME is hygroscopic and absorbs water from tank atmospheres, promoting microbial growth at rates significantly higher than conventional VLSFO. Here, the free-water monitoring frequency should be doubled for any tank containing a biofuel blend.
• FAME can cause filter blockage. Depending on feedstock composition, may be susceptible to crystallisation at lower temperatures. Therefore, Wax Appearance Temperature testing should be performed before re-activation for any vessel sailing to cooler latitudes post-Gulf.

Before returning to service

Reactivation without verifying fuel quality is the highest-risk point of the idle period.

The following should be completed before sailing:

• Confirm current laboratory results are in hand for all tanks in service -not older than 30 days at point of re-activation.
• Inspect and replace purifier and fine filter elements as a precaution if idle exceeds 90 days, regardless of visual condition.
• Ensure heating coils are operational and VLSFO service and settling tanks are at operating temperature before drawing fuel through to purifiers and main engine.
• For biofuel-blend tanks: perform Wax Appearance Temperature test before departure if the vessel will trade to temperate/ECA zones, or if the blend has been stored for more than 60 days. Additional tests such as Total Bacteria count (including yeast & mould), Copper & Steel Corrosion tests, and Chemical Species Analysis can be useful.
• Record all findings and actions in the engine log and retain all laboratory reports. These records can be critical for P&I and H&M insurers in the event of any machinery claim linked to fuel quality post-idle.

Vessels already returned to service

A number of vessels that were idle in the Gulf region have now resumed trading, in some cases without the opportunity to complete pre-departure fuel quality verification. The absence of immediate operational symptoms does not confirm that fuel quality is acceptable.

Sludge that consolidated in tank bottoms during idle can be disturbed progressively by vessel motion and fuel draw-down, causing filter blockages or purifier upsets days or weeks after departure.

Elevated cat fines cause liner and piston ring wear that accumulates silently and is not visible until lube oil analysis.

Owners and operators of vessels already back in service should arrange sampling of all tanks currently in use at the earliest opportunity and submit for full ISO 8217 analysis.

Precautionary measures in the interim: increase purifier throughput, increased frequency of filter inspections, plus elevated manual drain frequency. These actions reduce risk exposure but do not replace laboratory confirmation.

Article by Captain Rahul Choudhuri – VPS President of Strategic Partnerships, VPS; with editing by Bunker Index Staff