Some bunker deliveries at Singapore have contained excessive amounts of air, and as a result the quantity of fuel delivered and received was significantly overstated
UK P&I Club has published warning and advice to operators on the bunkering phenomena the 'Cappuccino Effect' :
This effect is termed "Cappuccino" as the entrained air causes the fuel to "foam" which makes traditional manual measurement at the time of delivery unreliable. After a few days the foam tends to collapse and tank measurements then show a significant "loss" of fuel.
The Club has issued guidelines compiled to assist ship's crew with identification of this potential problem and hopefully help with dispute resolution
A list of the recommendations is available here.