User charges have for some time, and especially in recent years, played an important role in financing federal programs. In 1991, user charges -- such as passport fees, national park entrance fees, and gasoline excise taxes -- amounted to nearly $120 billion and were the sole source of financing for some programs. This study documents the growth of user charges since 1980 and analyzes the economic and legal issues they have raised over the years as well as the more recent effects of changes in law and budget processes. Also assesses the potential for the growth of user charges. Charts, tables and drawings.