CRRC submitted the only bid in the tender with an offer of Baht 4.4bn ($US 121m).

Ridership on the standard-gauge link between Phaya Thai in central Bangkok, Makkasan and Suvarnabhumi Airport has surged since the line opened in August 2010 from around 30,000 passengers per day to more than 60,000. SRT subsidiary SRT Electric Train (SRTET) operates a mixture of express and stopping services on the eight-station line using a fleet of nine four-car Siemens Desiro EMUs.

SRTET says it needs to expand the fleet to meet demand and because the original trains are due for overhaul.