The group said it had been informed about fraud committed by senior employees at Singapore-based Dynamic Oil Trading (DOT) on Wednesday, and that "preliminary findings suggest a potential loss of around $125 million [750 million kroner, ed.]."
In a subsequent statement, OW Bunker said the losses could push it into bankruptcy after it had failed to reach an agreement with banks to keep it afloat.
"For the time being, the financial impact cannot be assessed. However, it must be assumed that the group's equity is lost," it said.
Separately, a review of OW Bunker's risk management contracts revealed a mark to market loss of around $150 million rather than the $24.5 million announced on October 23.
The company's head of risk management, Jane Dahl Christensen, had been fired immediately after the losses were discovered, it said.
OW Bunker was valued at 5.33 billion kroner (716 million euros, $890 million) in May in what has been Denmark's second biggest IPO in the year to date.
At the time the largest Nordic bank, Nordea, told investors the ship fuel supplier's business model was "robust and scalable," Danish news agency Ritzau wrote.