Petroleum refineries are the largest chemical industries that are responsible for the emission of several pollutants into the atmosphere. Benzene and its metabolites are regarded as the most hazardous compounds emitted by petroleum refineries. These contribute to toxic oxidants, which cause many serious health risks to petroleum refinery workers. This study aimed to analyze the effects of chemical exposure on hematological and biochemical parameters among workers at Zawia oil refinery and Mellituh oil and gas refinery companies. A total of 200 workers participated in this study which consisted of two equal groups (each group: n=100). The first group consists of petroleum refineries workers and the second group consists of non-oil work civil servants who were recruited as exposed and control subjects, respectively. The results of blood pictures, liver enzymes and kidney functions were compared between the groups. Mean white blood cell counts, platelet counts, and hematocrit counts were significantly higher, while the mean red blood cell count was insignificantly changed in petroleum refinery workers. The mean hemoglobin and corpuscular hemoglobin concentration levels were significantly lower, the mean corpuscular volume and mean corpuscular hemoglobin levels were insignificantly changed in petrol refinery workers. Liver enzymes and renal functions were significantly higher in petrol refineries workers. The present findings indicate that occupational exposure to benzene causes significant alterations in hematological and biochemical parameters and workers are at high risk of developing blood, hepatic or renal-related disorders. Protection and frequent medical attention should be given to petroleum refinery workers.