The technologically enhanced naturally occurring radioactive materials (TENORM), i.e., K-40, Th-232, and Ra-226 in waste petroleum scale, sludge, and produced water in Ma'rib Refinery - Yemen - were measured using spectroscopy with HPGe detector. To determining the radiation hazard of TENORMs in waste petroleum, The radium equivalent activity (Ra-eq), gamma-ray index (I-gamma), external radiation hazard index (H-ex), internal radiation hazard index (H-in), absorbed dose rate (ADR), annual effective dose (AED), annual gonadal dose equivalent (AGDE), alpha index (I-alpha) excess lifetime cancer risk (ELCR), and activity utilization index (AUI) are calculated to determine the radiation hazard of TENORMs in waste petroleum. The radiological data were analyzed using multivariable statistical methods to determine the discrepancies and similarities between the various samples. Frequency distributions have been studied for all radionuclides. There were fourteen variables measured in the data studied. The results of the Pearson correlation coefficient showed a positive correlation between all concentrations of TENORMs and all radiation hazard indicators. Factor analysis results in a two-component representation of the data obtained from waste petroleum samples. The dendrogram resulting from the Hierarchical Cluster Analysis divided the twenty-eight waste petroleum samples into three main groups using fourteen variables. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.