This research addresses the subject and practice of capacity building through professional development and career ladders in the petroleum (oil and gas) upstream or Exploration and Production (EP) sector. It focuses upon petroleum professions concerned with the evaluation, development and production of petroleum resources – notably petroleum engineers and geoscientists. The study adopts an insider action research methodology, with a particular focus on a national oil company – Petroleum Development Oman (PDO) LLC, which operates in the Sultanate of Oman. PDO epitomises a typical EP company undertaking significant professional development efforts across its sizeable pool of petroleum professionals. Despite its wide operational remit, however, there are some key issues that have affected the firm and that warrant scholarly interrogation. Notable amongst these are challenges in developing specialists, technical professionals and managers who are competent and able to address the increasing technical, developmental, commercial, and managerial difficulties facing the oil and gas sector. Consequently, this study seeks to propose actionable remedial strategies to address these managerial skills and organizational capability gaps. This research thesis offers valuable literature review of the concepts and practices related to capacity building, professional development, and career aspects. This has enabled bridging conceptualization gaps underpinning professional development and career management in the EP petroleum sector, particularly in PDO, and identifying elements and aspects that were considered in evaluating the studied case. Further, by examining PDO’s organizational records and codes of practice, the study has established the company’s intended strategies and approaches, hence allowing identifying gaps with practices as assessed by engaging PDO’s executives, team leaders, and professionals