The latest batch of Queensland Rail's trouble-plagued New Generation Rollingstock trains have been put on the tracks.
Chief executive Nick Easy said two of the locomotives started taking passengers on the Gold Coast and Airport lines on Monday.
It comes less than a month after the first three NGR trains were rolled out across the southeast network.
Mr Easy said he expected more of the 75 ordered to be put into service in the coming months as "further trains are deemed ready for service after completing comprehensive testing and safety assessments".
"This is another positive step in the rollout of the NGR program and delivering a modern, world-class rail network for southeast Queensland, including in lead up to the Commonwealth Games in April," he said in a statement on Tuesday.