Australia has about 1,500 military personnel in the Gulf
It is the first time such an admission has been made.
Defence Minister Brendan Nelson said that maintaining "resource security" in the Middle East was a priority for the government in Canberra.
But he added that the main reason troops were still in the Gulf was to ensure that the humanitarian crisis there did not worsen.
Australia was involved in the invasion of Iraq in 2003, and has about 1,500 military personnel still deployed in the region. There are no immediate plans to bring them home.
Releasing the government's review of its national security policy, Mr Nelson said that the supply of oil had influenced strategic planning.
"The defence update we're releasing today sets out many priorities for Australia's defence and security, and resource security is one of them," he said.
"Obviously the Middle East itself, not only Iraq but the entire region, is an important supplier of energy, oil in particular, to the rest of the world."
Critics have accused the Australian government of telling lies about Iraq.
Opposition politicians said that back in 2003, Prime Minister John Howard insisted the campaign to oust former Iraqi President Saddam Hussein had nothing to do with oil.
They have chastised Mr Howard, accusing him of making up his policy in the Gulf as he goes along.
Anti-war protesters say the government's admission has proved that the US-led invasion was more of a grab for oil rather than a genuine attempt to uncover weapons of mass destruction.
But ministers in Canberra have brushed aside the criticism, saying they remain committed to helping the US stabilise Iraq and combat terrorism.
They have also stressed that there will be no "premature withdrawal" of Australian forces from the region.