Minister for Defense Stephen Smith said Tuesday the government had sent a Letter of Request to the United States seeking cost and availability information for the aircraft, which would be obtained through the U.S. Foreign Military Sales program.
The Australian air force's fleet of four C-17As was obtained from the United States from 2006 to 2008.
The Defense Department said recent natural disasters in the state of Queensland and New Zealand have underlined the C 17s as an essential part of Australia's capacity to respond to emergencies within the country and the region.
The aircraft also support Australian and International Security Assistance Forces in Afghanistan and the Middle East, meeting their primary purpose in providing military long-range heavy airlift.
Smith said the decision to purchase the additional aircraft would be made following receipt of information from the United States.