While the alleged theft at Shell Singapore is believed to be the biggest of its kind in recent memory at a refinery, crimes surrounding marine fuel oil are not uncommon.
In July last year, eight men on a Singapore-registered tugboat were arrested after illegally selling marine gas oil worth $12,840 to a foreign-registered tugboat.
Four months later, ship-fuelling company Vermont UM Bunkering was the first firm to be charged with offences involving concealing benefits accrued from alleged criminal conduct.
The company and its directors had allegedly used invoices that falsely stated various quantities of fuel oil had been sold to Vermont UM Bunkering.
They were also believed to have sent out invoices stating that some marine fuel had been delivered when, in fact, the amounts were less than stated.
The case is still pending.
In 2014, the police noted a rise in marine oil theft in Singapore waters. Diesel was first stolen by Indonesian crew members from their own vessels, then sold to another vessel at almost half the usual price.
Crew from the buyer vessels, also Indonesians, then acted as middlemen and sold the fuel to another ship, outside of Singapore waters, at a slightly higher price, but still below market value.
In 2014, 60,000 litres of oil were exchanged illegally, a tenfold jump from 2013. The increase was mostly due to one incident involving 50,000 litres, a police spokesman said.
That year, a chief engineer of an oil tanker was convicted of criminal breach of trust when he tried to short-change his vessel of 200 tonnes of fuel.
He wanted to enter into a buy-back arrangement with an independent surveyor and a bunker clerk, where fuel is sold back to the supplier. The total value misappropriated then was US$125,400.
He was sentenced to 18 months in jail for criminal breach of trust. His sentence was reduced to 14 months on appeal.
An industry expert who did not wish to be named told The Straits Times that theft is not uncommon, "especially for small amounts (of fuel)", and has been going on for 15 to 20 years.
Such misappropriation usually takes place during the loading of fuel into the tanker, he added, where an extra volume of fuel on top of the stated amount is transferred.