Abstract: A method and apparatus for rejuvenating oil well drilling mud is provided by an endless filter which is supported by a pair of spaced driven drums; drilling mud is distributed onto a moving flight of the filter at spaced locations so as to provide layers of the drilling mud on the filter. Passage of the drilling mud through the filter is assisted by spraying the drilling mud with drilling mud which has passed through the system (filtrate) and by applying suction to the underside of the filter. The drilling mud, after passing through the filter is degassed in a second stage degasser. The filter is cleaned by a solution spray, and by back washing with air and either water or diesel oil.