The inquiry into the billion-dollar failure of Queensland Health's payroll system begins in earnest in Brisbane on Monday.

Two weeks of initial hearings will focus on the tender process, managed by the former Labor government, which saw IBM awarded the job.

The inquiry began with opening statements in February but the first witnesses will appear on Monday. They will be senior IT consultants from companies that lost the tender to IBM.

A government whistleblower last year claimed there was collusion, involving the government's internal IT provider CorpTech, to ensure IBM won the contract.

Retired judge Richard Chesterman QC is hearing the inquiry, which will look at the procurement and implementation of the problem-plagued system.

The probe, announced by the LNP government, will also look at whether any laws, contracts, or codes of conduct were broken, and why costs blew out so dramatically.

The system rolled out in March 2010 and was a spectacular failure. It left thousands of health workers underpaid, overpaid or not paid at all for months.

The original contract price was $6.2 million.

But by the time the system went live the amount paid to IBM was more than $37 million and the government had shouldered its own costs of a further $64 million to get it running.

The costs continued to climb dramatically after that, and a KPMG report, commissioned by the LNP government, has estimated it will ultimately cost $1.2 billion to fix and run the system by 2017.