A clear, practical, and comprehensive guide to capital investment evaluation, capital budgeting, and decision analysis. Designed for students and professionals alike, the book walks readers step-by-step through decision-making under uncertainty, emphasizing real-world application with numerous solved examples, illustrations, and end-of-chapter problems. With a focus on building foundational knowledge and critical thinking, this edition makes complex concepts accessible while encouraging a big-picture understanding of oil and gas operations. The book is ideal for those looking to enhance their ability to analyze, interpret, and defend economic decisions in capital projects. The Third Edition presents a unified volume combining both Deterministic and Probabilistic models, streamlining the approach from previous separate volumes. All time-sensitive materials, figures, and tables have been updated for clarity. Real-world examples have been added to enhance understanding of key concepts. Expanded sections include weighted average cost of capital (WACC), international economics, and abandonment costs. A new chapter addresses commerciality assessment and reserves booking, and an advanced depreciation technique has been introduced. Updated spreadsheet models support decline curve analysis, and all decision tree and Monte Carlo problems have been revised using the latest Palisade DecisionTools™ suite. In response to nearly two decades of user feedback, additional examples have been added for clarity. For instructors, a test bank of 300 questions and a set of 700 PowerPoint™ slides are now available.