The three men were working on the deck of the FR8 Venture when a large wave came over the bow as the ship entered the Pentland Firth, between the southern Orkney isles and the Scottish mainland.
Other crew members on the Singapore-registered vessel called the Shetland Coastguard at 12:40p.m and a lifeboat and rescue helicopter were sent to the scene, but a doctor winched on board found the two men dead.
The third was airlifted from the 42,000-tonne ship for treatment in hospital in Aberdeen, north-east Scotland.
Neil Cummins, watch manager at Shetland coastguard, said the tanker had loaded crude oil at the Scapa Flow terminal in Orkney and was headed for Houston, Texas.
There were westerly winds at the time of gale force eight (39-46 miles or 63-75 kilometres per hour) to storm force 10 (55-63 miles or 88-102 kilometres per hour) and a four- to five-metre (13- to 16-feet) swell, he added.
The nationalities of the dead and injured men was not immediately known, a coastguard spokesman told AFP. The incident has now been passed to Britain's Maritime Accidents Investigation Branch, he added.

Copyright AFP (Agence France-Presse), 2006