It is reported in standard cubic feet per stock-tank barrel. While a well is still above the bubble point and no free gas is entering, the producing ratio sits near the solution gas-oil ratio. Once reservoir pressure is below the bubble point, or a gas cap is coning into the perforations, the producing ratio climbs.
A rising ratio is one of the plain signs that a solution-gas drive is depleting, or that the completion is too close to a gas cap. Oilfield standard conditions for the gas volume are often 14.7 psia and 60 °F; a sales contract can name a different standard, and the two volumes are not interchangeable.