
The order completed an agreement to purchase the planes announced during the Paris Air Show in June.
"These additional Boeings will support our commitment to expanding our market presence while delivering profitable growth," said Piyasvasti Amranand, president of THAI.
"They set the standard for twin-aisle reliability because Boeing continuously incorporates new technology and innovations into the aeroplane to improve operating cost and plane performance. And, with a wider and more spacious cabin, the Boeing is preferred by passengers in every class."
THAI currently operates nearly every 777 model produced, and THAI Cargo became the first carrier in Southeast Asia to use the 777 Freighter.
Marlin Dailey, vice president of sales and marketing for Boeing Commercial Airplanes, said the firm thanked THAI for the trust and confidence it continued to show for aircraft built by the US company.
"We look forward to working with THAI in introducing the 787, as well as these additional 777s, into its operations."