The application of corrosion inhibitors are fundamental to the safe and reliable operation of carbon steel infrastructure, presenting one of the most cost effective methods of internal pipeline corrosion control when deployed correctly. Despite decades of application in the oil and gas industry, a number of gaps remain in relation to our fundamental understanding of the performance of inhibitors. This is particularly true in the context of partitioning, and more so when the system under consideration comprises multiple surfactants. Part 1 of this two-part paper provides a detailed insight into the fundamentals of surfactant partitioning. Initially, the role of micellization in influencing single surfactant partitioning/distribution behavior between oil and brine is discussed, providing theoretical explanations for single surfactant system responses. The complexity of the systems examined increases with consideration extending to multi-surfactant environments, accompanied by discussion of idealized theoretical behavior. Subsequently, an idealized model to predict multi-component distribution responses between oil and brine is presented. To explore the model’s capabilities, experimental partitioning and micellization data collected from previous studies for two benzyl ammonium chloride corrosion inhibitors (BAC-C12 and BAC-C16) is integrated into the model. Such integration permits investigation into the effect of surfactant concentrations, relative surfactant molar ratios and water cut on partitioning/distribution behavior.