Continued exploration for additional secure and domestic energy supplies is of fundamental importance for India. These current and future energy resources include petroleum (oil & gas) which is currently the dominant energy source, as well as new subsurface resources such as geothermal and natural hydrogen. The existence of all of these resources is controlled by subsurface geologic systems that are defined by a combination of particular geologic features, properties and processes. Successful exploration efforts depend on structured geoscientific analyses of these geologic systems which, in the case of oil and gas, are described as petroleum systems. In this chapter, essential data and definitions are provided, starting with global energy supplies and the current and future role of oil and gas. It is essential to understand the present and future status of both global and domestic energy supplies, and to adhere to definitions and standards that are applied to energy systems. Energy systems are always developing due to changes in supply, demand, availability, the introduction of new technologies, geopolitical scenarios, as well as the cost of the resources and their emissions. Transitions between different sources always occur and are usually on the scale of decades to centuries due to the size and complexity of the systems, and there is general agreement that a ‘global energy transition’ is currently underway to meet the combined challenge of increasing global energy demands and the need to reduce harmful emissions. Petroleum systems analysis is then introduced with topics including the history of the petroleum systems methodology, its fundamental role in structured exploration risking processes, the importance of models and process modeling, and the scale of exploration studies and risk assessments from basin to play to prospect. The chapter then concludes with a discussion of corporate application strategies for petroleum systems analysis and the required essential communications between technical experts and decision-makers.