Results of five separate studies investigating a total of 169 individual sources (16 industrial classes) of air pollution are reviewed in depth. Purpose of studies, done by five separate contractors was to: (1) assess the degree source controls fail to maintain continuous compliance with regulatory requirements, (2) present typical frequency, duration, and magnitude of excess emission data for a variety of industrial sources, and (3) identify the primary causes of emissions incidents. Report presents an overview of findings, a tabularized set of data with narrative for each category, and a set of recommendations for agencies wishing to control operation and maintenance problems.