Running immigration detention centres will cost the federal government $1 billion over four years.
Security company Serco negotiated a new four-year contract with the Department of Immigration before Christmas, going from $299.2 million over four years in 2009 to $1.03 billion, News Limited reported on Thursday.
A separate contract to manage the immigration residential program doubled from $44.5 million to $85.6 million.
The opposition has labelled the blow-out as a failed "stimulus program" for asylum seekers.
The variation of the contract with Serco - from 2009 to 2014 - was made on December 2 last year.
It had previously been valued in July 2011 at $715 million.
Immigration Department spokesman Sandi Logan said the original contract did not cover the expanded number of detention centre sites.
Immigration Minister Chris Bowen said the new contract would not impact on the federal budget.