The value of the order, which was placed on January 16, 2017, was not disclosed.
The six 19,700 dwt ships are expected to be completed in 2018.
Each of the six 12,000 gross ton ships will have a market value of around USD 26 million, according to data provided by VesselsValue.
The six new tankers will fly the flag of Hong Kong.
Raffles Shipping Group currently has a fleet of 57 vessels, comprising 15 bulkers, 41 tankers and one liquefied petroleum gas (LPG) carrier.