The South Australian Liberal government announced earlier this week it would soon release tenders for the operations of both services.

"Melbourne, one of the biggest metropolitan train networks in the country, outsource their operations and has shown how this model can deliver sustained improved efficiency and customer service outcomes," Transport Minister Stephan Knoll said.

He said Melbourne's rail system had experienced 85 per cent growth in the 15 years since 1999, while Adelaide's bus system patronage had grown just 15 per cent since 2001-02.

"The outsourcing of public transport services is a tried and proven model that leads to better services and increased patronage," Mr Knoll said.

"We know that outsourcing of operations is increasingly a preferred business model for delivery of public transport services around the world."

But opposition leader Peter Malinauskas said it was clear Adelaide commuters were more satisfied than their Melbourne counterparts.

"In Melbourne, satisfaction ratings are lower and fares have gone up," he said.

"Public trains and trams in Adelaide, Perth, Brisbane and Sydney all have higher commuter satisfaction ratings than the private trains in Melbourne."

Mr Malinauskas said Canstar Blue ratings of all capital city train services place Adelaide second and Melbourne last.

"Satisfaction ratings on public trains and trams are higher than private trains and trams," he said.

The state government has guaranteed service frequency and standards will be maintained and "strongly expects to be able to increase service levels" once the tenders go through.

Mr Knoll said the government will retain ownership of train and tram assets and continue to control the cost of fares.

Australian Associated Press