Abstract: A mud degasser is located in the mud return line between a well being drilled and a shale shaker mounted on a mud tank in order to degas all of the mud leaving the well. A variety of mechanisms operate on the mud to remove entrained gas. A major separating technique is to deliver the mud axially into a rotating pump impeller which slings the mud radially against the walls of the separator vessel. Other operating mechanisms include vibration and/or the application of a vacuum.