The Bloody Sunday inquiry has so far cost about £181m, Secretary of State Shaun Woodward has confirmed.
Soldiers shot 14 people dead in Derry on Bloody Sunday
Mr Woodward confirmed the figure during Northern Ireland questions in the House of Commons. About half of the cost has gone on legal services.
The inquiry was set up in 1998 to re-examine the events of 30 January 1972, when British soldiers shot dead 14 people in Londonderry's Bogside.
It is the longest and costliest inquiry in British legal history.
The first witness was heard in November 2000 and the last in January 2005.
Earlier this month, Mr Woodward said he did not believe the tribunal's completed report was "imminent".
A spokesman for the tribunal said the delay was due to the sheer scale of the operation - 2,500 witness statements, of whom 922 were called to give direct evidence.
There were also 160 volumes of evidence, containing an estimated 20-30 million words, plus 121 audio tapes and 110 video tapes.