It also announced stopping of non-stop flights on Singapore-Los Angeles and Singapore-Newark sectors, as it would remove from service five A-340-500s by next year-end.
Today's firm order commitments are valued at US Dollar 7.5 billion based on Airbus' published list prices. Deliveries are due to begin in 2017, an airline spokesperson said.
SIA now operates 19 A380-800 superjumbos and has already placed firm orders for 20 A-350s for delivery from 2015.
The latest A-350-900 variant, which has been selected for the 20 additional aircraft order, would be used on medium and long-haul routes, the spokesperson said.
"As part of the deal, Airbus has agreed to acquire SIA's five A340-500s, which will be removed from service in the fourth quarter of the 2013 calendar year, in line with the Airline's policy to maintain a young fleet.
"This will result in the cessation of non-stop flights between Singapore and Los Angeles and between Singapore and Newark, in the absence of replacement aircraft in SIA fleet with sufficient range and operating economics," she said.
SIA CEO Goh Choon Phong said, "Although disappointing that we will be halting these services, we remain very committed to the US market. Over past two years, we have increased capacity to both Los Angeles and New York by deploying A-380s on flights via Tokyo and Frankfurt."
With the new commitments announced today, SIA will have firm purchase or lease orders in place with Airbus and Boeing for 68 new widebody aircraft, including 15 additional A330- 300s and eight additional B777-300ERs ordered last year. This excludes 20 B787s on firm order.
