Defence Minister Jose Bono confirmed on Tuesday that the military deployment came with a price tag of $450 million, though the government had negotiated a favourable oil purchase agreement.
Of the total, three quarters went into military-specific expenses while the remainder went towards humanitarian aid pledged at an international conference on Iraqi reconstruction last October and that event's organisation.
Bono told parliament the bill included the cost of repatriating the 1430 soldiers sent to Iraq by the previous conservative government of Jose Maria Aznar.
Aznar, a solid US ally over Iraq despite overwhelming public opposition, saw his right-wing Popular Party slump to a surprise defeat by the Socialist Party in 14 March general election.
The defeat came just three days after deadly train bombings in Madrid which were blamed on Islamists in what was widely seen as revenge for Spanish participation in the US-led occupation.
Spain suffered 13 fatalities in Iraq, including two journalists.
Bono pointed to purchase rights for 15 million barrels of Iraqi crude oil reserved for Spanish energy firms Repsol YPF and Cepsa as the only upside to his country's participation in the Iraq campaign.
However, there is also an embryonic energy agreement between a US firm and Soluziona, an offshoot of Spain's Union Fenosa.