Ten pirates, armed with guns and knives, hijacked a Panamanian-flagged oil tanker off the Malaysian coast in the Straits of Malacca, according to the International Maritime Bureau.
The incident occurred near Malaysia's Pulau Kukup on Thursday.
The armed robbers forced the ship's master to steer the vessel to a spot where an unidentified orange hull tanker parked itself alongside forcing the crew to transfer gas oil from the vessel to their ship, the bureau's piracy reporting centre said.
The pirates tied up the crew and locked them in a cabin.
After stealing the gas oil, the pirates robbed the crew of their personal belongings and escaped.
The oil tanker became the second such vessel to be hijacked in Malaysian waters in four weeks.
In early October a Thai-flagged oil tanker went missing for two days after a hijacking before being released without its cargo.