Gas to Oil Ratio (GOR) is a commonly used term in the crude oil exploration and production industry. GOR is the ratio of volumetric flow of produced gas to the volumetric flow of crude oil for crude oil and gas mixture sample.
For any hydrocarbon mixture produced from an oil production well, the proportion of liquid and vapor phases in the mixture changes with changing temperature and pressure conditions. In order to compare the GOR from different oil and gas samples, the oil and gas flowrates must be considered at same temperature and pressure conditions. Hence the GOR is always specified at standard temperature and pressure conditions. The liquid and vapor volumetric flow rates are calculated at standard temperature and pressure conditions, expressed in sm3/hr.
Sometimes only the gas volume is expressed at standard conditions and liquid volume is expressed in barrels. Then the GOR is expressed in sm3/bbl. But it is still important to calculate the gas and liquid volume at standards conditions, even if later they are converted to other units only for reporting purpose. If a hydrocarbon producing well produces high GOR mixture, it is identified as a gas well. If GOR is low, it is identified to be an oil well.