Boeing and Dubai-based Emirates Airline Sunday announced an order for 50 extended-range Boeing 777-300s, plus options for an additional 20 of the twin-aisle commercial jetliner.

The order, valued at $18 billion, makes it the single largest commercial airplane order in Boeing’s history by dollar value, according to a Boeing Co. press release.

It also makes 2011 the best-selling year for the 777 program, surpassing the previous record of 154 orders set in 2005. With the Emirates order, the 2011 net order book for the Everett-built 777 currently stands at 182. The options for 20 additional airplanes is valued at $8 billion.

Boeing’s announcement came just before its release of a forecast that airlines in the Middle East will need an estimated 2,520 airplanes worth $450 billion by 2030.

Single- and twin-aisle airplanes will account for 90 percent of the Middle East’s new airplane deliveries over the 20-year period, according to the Boeing forecast.

An estimated 1,160 single-aisle jets, such as the Boeing 737 MAX, and 1,110 twin-aisle airplanes, such as the Boeing 777 and 787 Dreamliner, are expected to be delivered to the region during this time, according to Boeing.

The remaining 10 percent is split between large airplanes such as the Boeing 747-8 Intercontinental and will account for 7 percent of projected demand, with an estimated 180 airplanes to be delivered to airlines in the Middle East. Regional jets will account for the remaining 3 percent.

“The 777’s reliability, performance and operating economics have firmly established it as the backbone of our fleet,” said His Highness Sheikh Ahmed bin Saeed Al Maktoum, chairman and chief executive, Emirates Airline & Group. “We have an ambitious and strategic plan to continue growing our international network and especially increasing our long-haul, non-stop routes.  This order supports our fleet expansion and reiterates our commitment to operating a modern fleet for the benefit of our passengers and to ensure operational efficiency as well.”

Emirates is the world’s largest 777 operator with a fleet of 94 777s through direct purchase and lease, plus additional unfilled orders on backlog for 41 777-300ERs previously on order. It is also the only airline in the world to operate every model in the Boeing 777 family, including the 777 Freighter.