A protocol was developed to evaluate collector performance in the laboratory under condition, that stimulate plant practice Eight collector manufacturers provided nine samples of their products, each designed to handle 1700 m3/hr (1000 ft3/min) of airflow. Each collector was tested using mists of mineral oil, soluble oil, and synthetic fluid; for a three stage collector, tests with each metalworking fluid lasted for thirteen 24- hour days. For each collector stage as well as for each assembled collector, tests established the relationship between efficiency and droplet diameter for droplets from less than 0.3 to about 6 μm in diameter. Substantial differences in efficiency arid pressure drop were found among the stages and assembled collectors. Some metal mesh filters worked well as first stages, whereas pocket filters, one cartridge filter, and an electrostatic precipitator worked well as second stages. High-efficiency particulate air (HEPA), 95% d octyl phthalate (DOP), and candle filters provided excellent efficiency as final stages for droplets of all sizes. When collecting mineral oil mist, the efficiency of some first and second stages deteriorated substantially over the relatively short term of these tests.