Those interested have until December 4 to register under the tender process.

In July this year, Treasurer Wayne Swan announced $3million had been set aside to do the detailed planning work needed to obtain a cost and determine the project's viability.

Infrastructure Minister Anthony Albanese said the proposed rail line project would involve building a 35-kilometre standard gauge rail line connecting the Illawarra Line from Wollongong to the Main Southern Line running from Sydney through Campbelltown.

``The allocation of additional funding followed the findings of the pre-feasibility study published earlier this year, namely that completing the rail line has long-term economic merit but more work needed to be done before sensible investment decisions could be made,'' Mr Albanese said.

``The feasibility study will assess existing infrastructure, engineering requirements and likely demand for the proposed line, as well as undertake detailed economic and financial modelling.''

The feasibility study is expected to take about 18 months to complete.