OBJECTIVES: The purpose of this study was to review the status of used engine oil collection in the United States. By conducting the study@ the American Petroleum Institute wished to document state efforts to collect oil and the outcomes of such efforts. By doing so@ the Institute hoped to provide examples of how used oil collection can be successful as well as warning of the pitfalls that should be avoided based on the experiences of other states. An early objective of the study was to evaluate the existence and success of programs on a state-by-state basis. Unfortunately@ other than in general terms@ this task is impossible due to diverse data collection methodologies utilized by the states. Even in well-established programs@ data about used oil collection is acquired in a variety of different ways. For example@ some states require collection centers to provide very specific data up to four times each year. Other states rely on data provided by used oil haulers@ and this data almost always includes industrial@ commercial@ and vehicle used oils. As a result@ comparability between states is difficult. This study provides the best data available as of the summer of 1995. In an ideal situation@ the costs of programs could be compared to the amount of used oil collected. However@ with inconsistent data collection@ this is impossible to do beyond determining@ in general terms@ a few factors that make programs more successful. Initially@ the developers of this study had hoped to rely solely on information provided by the states. However@ other sources have been utilized in order to fill in any gaps that may have existed@ to attempt to adjust any distorted data@ and to provide a more complete picture of national used oil collection efforts. Other sources are indicated as they are discussed in the study.