This document presents the financial environment associated with the exploration and extraction of hydrocarbons. The main theme of the article is the description of the most common practices used in this sector of the economy. Exploration and extraction normally require significant financial resources required for the implementation of seismic operations, exploration, assessment, production drilling, and associated infrastructure. That is why even the owner of an exploration concession which has sufficient financial resources may be reluctant to invest them entirely in the concession area. This paper describes the reasons for investors' involvement in many upstream projects in return for partial rights in the extraction - either rights to physical materials flow or financial income. This analysis draws attention to the need for diversification and optimization of the assets portfolio. It also focuses on the behaviour of oil and gas companies that gladly give away some of their rights in the exploitation concessions (through the Farmout Agreement, Joint Operating Agreement, Exploration Agreement) even in the most promising geological areas in order to gain interests in assets which are often potentially less attractive but more predictable in terms of political risk. Additionally, the paper determines why oil and gas companies try to maintain or gain the position of the Operator and have the biggest impact possible on the operational management of exploration projects. Sometimes they settle for being one of the concession holders, controlling the execution of works from the level of Operational Committees. The paper concludes that, for upstream companies, the results of the whole portfolio of upstream assets are much more important than the success or failure of a single project.