Used to sum up oil, gas, NGL and condensate resource volumes. This estimate will not be exact, but can be carried out using one property as the basis. Energy, mass, volume or value are possible approaches. The Norwegian Petroleum Directorate uses a volumetric conversion of NGL and oil to liquid and a simplified energy-based conversion factor between gas and liquid. The relevant conversion factors are: 1000 Sm3 gas corresponds to 1 Sm3 o.e. 1 Sm3 oil corresponds to 1 Sm3 o.e. 1 tonne NGL corresponds to 1.9 Sm3 o.e.