The Gas Hold-Up Logging Tool (GHT01) measures the gamma rays emitted by a 3-millicurie cobalt radioactive source located at the bottom of the instrument. The gamma rays are scattered by the surrounding liquid and detected by the instrument probe. Since gamma ray scattering is higher in liquid than in gas, it can reflect the gas hold-up condition of the liquid. The tool registers a higher count in the liquid phase and a lower count in the gas phase, making it effective in reflecting the gas hold-up in vertical, inclined, and horizontal wells.