This book examines the cross-country and country-level economic performance of OPEC member countries, and tests the impact of natural capital, financial capital, and institutional management framework on the economic output levels of these countries. The research study also evaluates the impact of standard neoclassical production factors of physical capital and labour on the economic performance of these countries. These oil-producing countries have largely been ignored in contemporary empirical studies and published literature on economic growth and performance, even as the impact of their vast natural capital in the form of significant petroleum resource endowment and the related production and pricing implications continue to dominate and drive global economic systems and conditions. This research study specifies and tests linear regression models with gross domestic product per capita as the dependent variable and extends the standard neoclassical and endogenous growth models to include the new independent variable factors of natural capital, financial capital and institutional management framework.