Oil and gas industry is complex and competitive and its projects are characterized by their importance and complexity. To achieve sustainability, oil and gas firms have to initiate and complete projects to scope, schedule, cost and quality. Hence, efficient Project Management Methodologies (PMMs) play a crucial role in successful project delivery. A conceptual model, adopted from the literature, was used to assess the influence of PMMs on project success. Based on a questionnaire data from 95 project management practitioners within the oil and gas industry in the Kingdom of Bahrain, correlational and regression analyses were used to test the research hypotheses. The quantitative study was backed with 17 semi-structured interviews to obtain in-depth understanding about the organizational PMMs. The major finding of the study revealed that applied PMMs have higher influence on project success in comparison with comprehensive PMMs. The companies in the oil and gas industry in Bahrain need to pay sharper attention to their methodologies and get them evolved with time to achieve higher success rates.