Abstract: Organic solvents, such as petroleum ether and gasoline, are used as extracting agents to measure oil content in oilfield waste water and the normal curves of reference oil are plotted. Studies of several extracting agents discover that different extracting agents and instrumentations can directly result in different normal curves of reference oil in the same block. It is proposed that petroleum ether should be preferentially used as the organic extracting a-gent and spectrophotometers of the same type should be used.