The stability of marine fuels is traditionally a very hot topic, especially in the beginning of so-called sulphur cap. The sulphur cap is the process of reducing the maximum level of sulphur content (from 3.5 to 0.5 wt%) in marine fuels, which are being used on deep sea from the first of January 2020. After this change, the large amount of marine fuels will be produced as a mixture of two or more components to achieve required sulphur level. Higher amounts of cutter stocks will increase the likelihood of decreased stability or compatibility of the marine fuels. Therefore, a reliable stability tests or their combination will be very important for marine fuels evaluation. However, only total sediment after aging is defined as a standard method according to ISO 8217 for stability testing. This method is not suitable for all the analysed marine fuels, so we verified using of microscopy for this type of evaluation. The set of marine fuels samples was tested using microscopy, results were processed and correlated with other selected qualitative parameters. The microscopy was evaluated as a suitable method for testing of marine fuels stability. This method could be used for very fast evaluation in industrial as well as research laboratories in combination with standard methods.

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