Manufacturing disturbances are inevitable in the fabrication of integrated circuits. These disturbances will result in variations in the delay specications of manufactured circuits. In order to capture the impact of these variations on the delay behavior of these circuits we propose a pair of statistical delay models for use inlogicdesign. These models abstract the real variations from the process level and can be used for statistical delay analysis and optimization in logic design and synthesis while oering an eciency vs. accuracy tradeo.