Principles and Theory of Oil and Gas Accounting (First Edition) is a textbook on Oil and Gas Accounting covering the Principles, Theory and practical Applications of Oil and Gas Accounting in Oil and Gas operating Companies around the World. Emergence of this book Principles and Theory of Oil and Gas Accounting is as a result of our training in B. Sc, M. Sc Accounting and our various researches in the field of Oil and Gas Accounting during our Ph.D research works and our practical experience gained through consultancy services in Oil and Gas related Companies. Oil and Gas Accounting is a relatively new area in conventional Accounting studies. Although, Oil and Gas prospecting, exploration, development and production dates back to 1950s in Nigeria and about 1830s in United States of America and other Countries in the World. This book s main objectives are to contribute to knowledge and to promote further research in Accountancy studies.