These samples have acid number higher than 1 mg KOH/g fuel while the port average acid number is 0.9 mg KOH/g fuel.
As can be seen, the percentage has increased significantly: in March, only 6% of samples had acid numbers above the port average, whereas in April and May (up to 13 May), approximately 30–40% of samples exceeded the port average.
| Month | % of Samples with Acid Number Higher than Port Average |
| January | 13% |
| February | 1% |
| March | 6% |
| April | 32% |
| May | 40% |
While it is often stated that there is no direct correlation between acid number and machinery problems, acid number can still serve as a useful indicator that further fuel quality assessment may be required. When the acid number of samples is higher than the historical average for a particular port, especially considering the recent changing trends in port data, further investigation of the chemical composition using techniques such as GCMS may be beneficial.
GCMS analysis of four samples bunkered in April and May from ARA ports revealed the presence of phenolic compounds, including 5-Pentyl-1,3benzenediol and 5-Methylresorcinol at concentrations higher than 20,000 ppm, oxygenated compounds above 2,000 ppm, and short-chain fatty acids above 500 ppm. To date, no operational problems related to these fuels have been reported to us.
In early 2025, VLSFOs with approximately similar chemical fingerprint components resulted in several operational issues onboard vessels. Although the chemical fingerprint of these new 2026 fuels does not completely match the fuels from early 2025, certain similarities have been identified.
Based on these findings, we strongly recommend close monitoring of machinery when operating on fuels bunkered in ARA ports that exhibit elevated acid numbers. Routine testing of Total Acid Number (TAN) and GCMS analysis for fuels with elevated acid numbers is advised to help mitigate the risk of operational issues.
This document does not reflect the overall quality of fuel being supplied in ARA ports.
Please do not hesitate to contact us if you require any further information or assistance.