Railway operators running commuter services in Auckland and Wellington will have to bid for the use of new electric rolling stock, the Government said today.

Transport Minister Steven Joyce released details of the way the services will work in the two cities as new electric rolling stock arrives.

Mr Joyce said the rolling stock, bought by the Government, would be held in special KiwiRail subsidiary companies and leased to train operators who provided the service.

KiwiRail would be able to bid to operate the services alongside other train operators, but all bidders would face the same price to lease the trains and to access the track.

KiwiRail currently operates the commuter rail services in Wellington, while private company Veolia operates them in Auckland.

"This move will ensure that while KiwiRail owns the trains, it is not necessarily the case that they operate the services," Mr Joyce said.

"Performance-based contracts ensure the train operator is rewarded for providing reliable services and penalised when they don't.

"We will ensure that operators have sufficient control over their operations to ensure they can be held accountable for performance."

Mr Joyce said the system would "build significantly" on the best of what was already in place and provide a strong base for quality commuter services.