Chicago-based Boeing and Ethiopian, Africa's largest cargo operator, made the announcement at the biennial Dubai Air Show, which continues through Thursday.
Boeing 777 freighters have a list price of $325.7 million. However, airlines and manufacturers typically negotiate discounts on such deals.
Later Tuesday, Airbus announced the tentative sale of the A320neos to Golden Falcon Aviation, the exclusive airplane provider to Wataniya Airways. Wataniya, a private company, resumed operations in July after the company folded in 2011 over financial difficulties amid the Arab Spring protests that gripped the Mideast.
At list price, the 25 A320neos would be worth $2.7 billion. Two-engine, single-aisle A320neos can seat a maximum of 180 passengers.
This year's air show has seen less sales than in past years. The only major deal announced so far came Sunday, when long-haul carrier Emirates purchased 40 Boeing 787-10 Dreamliners in a $15.1 billion deal.
So far, there's been little news for Airbus, which has pinned hopes of continuing production of its A380 double-decker jumbo jet on Emirates, the world's largest operator of the aircraft. Reports circulated before the air show that a major A380 sale would be coming.
Airbus employees even filled a news conference on Sunday, expecting the A380 sale, instead to find state-owned Emirates making the deal with Boeing in front of Dubai's ruler, Sheikh Mohammed bin Rashid Al Maktoum.
Emirates now relies solely on the Airbus 380 and the Boeing 777 for its flights, making it the largest operator of both. It now has 165 Boeing 777s in its fleet today and took possession of its 100th A380 earlier this month.
Also at the Dubai Air Show, Egypt's flagship carrier EgyptAir signed a letter of intent to order 12 Bombardier CS300 passenger aircraft for $1.1 billion.
The tentative agreement, signed at a ceremony at the airshow, also includes purchase rights for an additional 12 aircraft, which would double the value of the sale.
The U.S. Commerce Department has imposed harsh duties on Bombardier, charging the Canadian company of selling the C Series planes in America below cost and receiving government subsidies. In October, it said it would impose an 80 percent duty on top of duties of nearly 220 percent on the aircraft, a benefit for rival Boeing.
After the decision, Bombardier sold a majority stake in its C Series jet business to European aerospace giant Airbus for no cost.
Associated Press writer Brian Rohan in Cairo contributed to this report.
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