In this work the Pressure Index, created from the conjunction of the refining margin and the price differentials of the physical oils, will be described. This index is intended to reveal possible mismatches between the ICE Brent benchmark price and the various traded physical oils. As the benchmarks are influenced by several other economic factors, not only from the current supply and demand data, from time to time, abnormal movements occur. It is also expected that attempts to manipulate the benchmarks will become explicit. The Pressure Index seeks to demonstrate the role of the differentials in the identification of the current equilibrium conditions of the physical market in relation to the financial market. On the beginning, there is a brief description of the market and its historical evolution. Key agents will be introduced and their roles described. In Chapter 3, the North Sea market and the mechanics of its main benchmarks will be presented. Attention will be paid to the complex instruments that connect the physical and financial dimensions of the market. In Chapter 4 it will be described how the operation of the market takes place from the negotiations based on differentials or spreads. In the final chapter, the Pressure Index will be introduced. The focus of this work will be on the definition of the Index as well as on the application of the theory in a case study of the Colombian petroleum Castilla. In this way, we can define this work as a qualitative case study.