The paper discusses EPA's Data Attribute Rating System (DARS), developed by EPA to assist in evaluating data associated with emission inventories. DARS disaggregates emission factors and activity rate, then assigns a numerical score to each component. Each score is based on what it is known about the factor and activity parameters; e.g., the specificity to the source category, the spatial (geographical) congruity, the measurement or estimation techniques employed, and the temporal congruity. The resulting emission factor and activity rate scores are combined to reach an overall confidence rating for the inventory. The individual rating components are presented, and the attribute evaluation techniques are discussed. the development rationale and history are described, and recent enhancements (E.g., DARS software) are presented.