The planes will be used on the airlines' long-haul routes

The world's second-largest airline by market value said the deal was part of its fleet renewal programme.

Eighteen are firm orders for delivery between 2006 and 2010, while options have been taken on an additional 13 of the extended-range aeroplanes.

The airline will use the crafts on its long-haul and medium-haul routes.

The airline said competition between Boeing and its rival Airbus for the order was "very keen" but the B777-300ER "was chosen for its higher operating efficiency ( and) commonality with existing fleet and cabin spaciousness".

The planes will be powered by GE90-115B engines from General Electric.

Earlier this year, Singapore Airlines introduced the world's longest non-stop commercial flight, direct between Singapore and Los Angeles.

It then surpassed the record with a non-stop Singapore to New York flight in June.