This report describes a study to identify factors that influence exposure to volatile organic compounds (VOCs) and VOC mixtures. Dr. Stuart Batterman at the University of Michigan–Ann Arbor and colleagues used the extensive data that HEI posted on the Web from the Relationships of Indoor, Outdoor, and Personal Air (RIOPA) study (HEI Research Report 130 Parts I and II), and data from the National Health and Nutrition Examination Survey (NHANES), to characterize exposure distributions for 15 VOCs, with an emphasis on high concentrations. Factors examined included geographic location, weather, characteristics of participants' homes, and specific activities, such as pumping gas.