GAO said in a report published Monday those five GPA parties include Canada, Japan, Norway, South Korea and the European Union.
The report also showed that the U.S. recorded $1.7 trillion in total government procurement contracts in 2010, while the five largest GPA partner countries reported $2.4 trillion in contracts combined.
The agency also found lapses in the way U.S. free trade agreement and GPA partner countries statistically report government procurement data.
GAO noted that countries that participate in the North American Free Trade Agreement have not shared government procurement-related information since 2005.
The congressional budget watchdog offered several recommendations to the U.S. Trade Representative to change the way it reports government procurement data under U.S. FTAs and GPA.
These include collaboration with GPA parties to build up reporting processes, resume data exchange with NAFTA partners and facilitate proper documentation and review of U.S. statistical reports to the WTO.