Refining margins, also known as cracks, for the benchmark gasoil grade fell to $13.16 a barrel over Dubai crude during Asian trading hours on Monday, their lowest since Dec. 28.

The cracks for gasoil with 10ppm sulphur content were at $13.35 a barrel on Thursday. The markets were closed on Friday due to the Good Friday holiday.

Crude oil prices jumped on Monday as the United States looked set to announce that all buyers of Iranian oil must end their imports or be subject to sanctions.