Gas hold-up is one of the most important hydrodynamic characteristics that is needed for performance estimation, design and scale-up of reactors. The performance of large-scale reactors can be reliably evaluated by measuring the gas hold-up in such reactors. In the present work, local gas hold-up in an industrial reactor has been measured with the help of gamma ray tomography. Based on these measurements, an empirical equation has been proposed for the estimation of the gas hold-up distribution. The proposed equation has been validated by comparison with laboratory scale data.