Around £144 million was spent on external consultants by the Northern Ireland government in five years, an Audit Office report said.
Expenditure peaked in 2006/07 at £42 million but has since fallen to £19.5 million, the review said.
Consultants were called in for jobs departments or other public bodies did not have the expertise for, such as designing assessments for use during staff promotion processes.
The report did note significant improvement in use of competitive tendering but highlighted some cases where contracts were not the subject of bids.
It said: "Skills transfer is essential in addressing departments' future reliance on external consultants and securing better value for money.
"We recommend that business cases should always give explicit consideration to the transfer of skills."
Over the period 2005/06 to 2009/10, Northern Ireland departments including agencies, non-departmental public bodies and health trusts spent £144 million on external consultancy. Expenditure peaked in 2006/07 at £42 million but fell to £19.5 million in 2009/10.
The 55-page report by auditor general Kieran Donnelly - Use Of External Consultants By Northern Ireland Departments: Follow-Up Report - made nine recommendations.
In June 2004 the Audit Office published a report on the use of external consultants and found that departments were failing to comply fully with DFP guidance and that there was considerable scope for improvement of procurement and management of external consultancy services. This follow-up study examined the improvement since then.
The Audit Office added: "Departments have demonstrated a significant improvement in compliance with DFP guidance and good practice, In particular, there has been greater compliance in the preparation of business cases, adherence to competitive tendering arrangements and completion of post-project evaluations."