Placing Sydney's entire bus network in the hands of private operators could result in almost $500 million in savings over five years, a report commissioned by a transport lobby group estimates.

A renewed push from the Tourism and Transport Forum for private firms to expand their reach comes weeks after the acting Auditor-General found the privatisation of Sydney's ferries was justified, pointing to about $100 million in savings since 2012.

State-owned Sydney Buses carries the majority of the city's passengers. Credit:Brendan Esposito

In releasing the latest report, the forum's chief executive, Margy Osmond, said it made the case clear that private operators should be given the opportunity to competitively bid for the four contracts held by government-owned Sydney Buses.

"Our analysis indicates that there is the potential for up to half a billion dollars in savings over five years if Sydney Buses was run by a private operator," she said.