America's port infrastructure is vital to U.S. foreign trade and a bulwark for national security. One way the federal government funds port-related programs is to levy user fees. GAO was asked to examine (1) what is known about the way selected fees assessed on air and sea port users are set, collected, used, and reviewed and (2) the effects of these attributes on program operations. GAO examined the Harbor Maintenance Fee (HMF), the Merchandise Processing Fee (MPF), and the Customs, Immigration, and Agricultural Quarantine Inspection (AQI) user fees assessed on air and cruise passengers and commercial vessels using criteria that have often been used to assess user fees and taxes--equity, efficiency, revenue adequacy, and administrative burden. The port-related fees GAO examined vary in how they are set, collected, used, and reviewed, creating misalignments between the fees and corresponding services, as well as administrative and oversight challenges. Although the customs, immigration, and AQI inspections have largely been consolidated under U.S. Customs and Border Protection (CBP), the corresponding fees remain separate and distinct and differ in how the rates are set and adjusted, the portion of costs they recover, and on whom the fees are levied.