New figures show that candidates in this year's General Election disclosed election expenses of €9.3m.
That figure represents a decrease of almost 16% on the figure reported for the 2007 election.
Fine Gael spent €3.1m, followed by Fianna Fáil with €2.1m.
Labour's election costs amounted to almost €2m, while Sinn Féin's figure totalled almost €500,000.
The Green Party - who failed to have any candidate elected - spent almost €250,000.
The figures were published by the Standards in Public Office Commission which said 23 candidates face possible prosecution for breaching ethics legislation.