Produced water is excess water from oil production, which contains hydrocarbon residues and other pollutants. One method that can be used to treat wastewater is the construction of artificial wetlands. The Rima Water Treatment Project (Oman) is a constructed wetland that was recently implemented to biologically treat produced water. In this study, the abundance and diversity of oil-degrading bacteria across the wetland system were evaluated and compared to water quality, as it progressed through four subsequent terraces in three parallel tracks of the wetland. In addition, oil-degrading bacteria have been isolated and characterized based on their ability to withstand different environmental conditions. The chemical properties of the sample were measured, including the oil content in water, pH, EC, total elemental composition, and hydrocarbon compounds, using gas chromatography-mass spectrometry (GC-MS). Culturable bacteria were enumerated using nutrient agar, Bushnell Haas mineral salt (BHMS) agar, and mineral salt medium (MSM) as minimal media. Morphologically different bacteria were isolated and tested for their ability to degrade crude oil using a MicroResp™ system. The strains with the highest oil degradation rates were further tested for their ability to withstand high ionic strengths, a broad range of pH, and their response to NPK fertilizers using growth curve analysis. The strains were then tested for their ability to form biofilms. Microbial diversity was assessed by 16S rRNA V4 gene sequencing in the Rima wetland system. Our findings showed that the oil-in-water content decreased to less than 1 ppm at the end of the wetland. In contrast, EC, pH, and minerals such as Na progressively increased as they flowed through the four stages of the wetland. Most hydrocarbon compounds decreased as they progressed through the system. Moreover, the bacterial enumeration progressively decreased, being highest in the first terrace. Interestingly, there was also a significant difference in bacterial enumeration between the three parallel tracks. Oildegrading bacteria were more abundant in the first two terraces of the wetland and in the second and third tracks. The isolated bacteria were all able to use crude oil as a carbon source. Shewanella sp., Aeromonas sp., Aeromonas hydrophila, Ochrobactrum sp., and Enterobacter sp. had the highest respiration rates. However, Ochrobactrum sp. is a strain that is tolerant to different pH ranges, high salinity, responsiveness to NPK, biofilm formation, and order of oil degradation. The 16S rRNA diversity showed higher bacterial diversity in the last stages of the wetland system, with an overall very low number of archaea. Even though the differences in Shannon and Evenness diversity indices between the terraces were small, the number of bacterial classes and community structure were significantly affected by both terraces and tracks. The most abundant class observed in the initial stages of the wetland was Alphaproteobacteria, where most of the oil degradation took place. Bacterial community 2 (clustered by correlation) was responsible for the oil degradation and was dominated by Rhodobacter, Loktanella, and Thiofaba genera. Cyanobacteria negatively correlated with hydrocarbon degradation. Further studies are needed to investigate the effects of autotrophic bacteria on the removal of different hydrocarbon compounds. To increase the efficiency of wetland systems, further cross-inoculation and bioaugmentation trials can be conducted using the identified oil degrading bacterial isolates.