Omans Transport & Communications Ministry has issued a tender for legal consultancy services for the national railway scheme.
The deadline for bids is 20 January.
The scope of work involves preparing the laws, rules and regulation and other institutional requirements for the railway.
Oman has not yet confirmed whether it will operate the rail services itself or bring in international operators.
UK-based Grant Thornton was appointed to provide advisory services for the establishment of operator Oman Rail Company in 2013.
The design-and-build contracts for the first 207-kilometre phase of the 2,244km, $15bn scheme are currently out to tender, with technical bids due on 18 January and commercial bids on 1 March. The railway is due to start operations in 2018.
The railway is to be built on uniquely challenging terrain, requiring multiple bridges, tunnels and underpasses. This led the 18 contractors prequalified for the three design-and-build deals to request more time to prepare their bids.
The planned railway forms part of a wider investment programme to improve Omans transport links.