Hundreds of millions of dollars in financial errors have been revealed in an audit by the WA Government's financial watchdog.

Western Australian Auditor-General Colin Murphy found 476 mistakes made by different agencies, which resulted in the Government's assets being overstated by more than $130 million.

The Government's surplus was also amplified by about $70 million.

In total, about $350 million worth of errors were identified.

Mr Murphy said while the audit identified the mistakes before the agencies published their final figures, they were still significant.

"If there are errors in those amounts, then the agencies don't have a true picture of their financial position," he said.

"Agencies also provide, throughout the year, updates to Treasury about how the state's travelling, so if they have errors then Treasury is not getting a clear picture.

Mr Murphy also found some agencies experienced "significant problems" after the decommissioning of the controversial Office of Shared Services (OSS), although most transitioned successfully.

The OSS was a government department that was supposed to save money by combining public service administration and payroll functions but ended up costing more than four times the initial estimate of $80 million to set up.

In December the Government said it had spent a further $90 million decommissioning the project.

The Auditor-General said three agencies received qualified opinions on their financial controls.

One was unable to complete its financial statements and table its annual report within the time frame required by law.

Agencies pay out too much on some redundancies, report finds

Mr Murphy also found the Government spent more than it should have on redundancy payouts for public sector employees.

The report examined voluntary severance packages given to more than 1,000 employees from different government agencies.

It found the cost of the payouts was almost $120 million.

Mr Murphy said the audit identified inconsistent methods of calculating the sum of the payout in different agencies, resulting in some employees receiving more money than necessary.

He said while it was impossible to quantify the cost of the inconsistencies, the final cost was higher than it should have been.

"Certainly the number is greater, there is no doubt about that, than it should of been," he said.

"We've certainly taken steps with the Public Sector Commission to make sure the rules have been reinforced."

Mr Murphy's report also suggested that if the complexity of reporting requirements for small agencies was reduced, significant savings could be achieved.