The contract was signed by Emirates chairman Sheikh Ahmed bin Saeed Al-Maktoum and the head of Boeing Company's commercial aircraft division, Alan Mulally, at the Farnborough Air Show, which is under way near London.

The first four 777-300ER (Extended Range) aircraft will be delivered during 2006, while the purchasing rights for the other nine extend through 2012, Emirates said in a statement.

Sheikh Ahmed said: "The 777 has proved to be an excellent aircraft for Emirates, and is extremely popular with our passengers, cargo customers and crew.

"The new Extended Range version will provide the reliability and the extra capacity for passengers and cargo which we will need. The low operating costs, renowned passenger approval, and the revenue capability from both cargo and passengers are the main reasons we selected the 777-300ER."

The 777-300ER has a flight range of 8,900 kilometres (5,563 miles), against 6,700 kilometres for the standard 777-300.

The deal allowed Emirates and Boeing to take centre stage in terms of civil aircraft order announcements in the opening hours of the week-long biennial Farnborough show, a traditional battleground for firms vying for orders and publicity.

The airline, which currently operates a mixed fleet including 21 Boeing 777-300s and 777-200s, said it would use the new planes to further its expansion and increase frequency on major trunk routes.

Next year it will take delivery of a separate batch of 26 777-300ERs from leasing companies as announced at the Paris Air Show last year, and by late 2007 will have a total of 51 Boeing 777s.

"When Emirates receives the 777-300ER, it will become one of three airlines in the world operating four members of the 777 family," said Boeing's Mulally.

"That's further evidence of its commitment to be one of the world's premier airlines."

Launched in October 1985 with two leased aircraft, Emirates expects to have a mixed fleet of 169 Boeing and Airbus planes by 2012.

The airline, which has been profitable in all but its second year of operation, also has 43 Airbus planes in service and 70 more on order including 45 of the new superjumbo A380-800s.

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