Ratio of the volume percent oil to the volume percent water in an oil mud, where each is a percent of the total liquid in the mud. OWR is calculated directly from the retort analysis of an oil mud. For example, if a mud contains 60 vol. % oil and 18 vol. % water, the oil percentage is (60/(60 + 18))100 = 77% and the water percent is (18/(60 +18)) = 23%. That OWR is written as 77/23.