With the growing share of renewable energy and emerging technologies, establishing and maintaining adequate flexibility is an important part of Thailand’s power system development and modernisation, and the country’s clean energy transition. Power system flexibility is crucial for ensuring security of supply. Thailand’s power sector has two main avenues to enhance its flexibility. One is to enhance the technical flexibility of the system. The other is to change or reform commercial and contractual structures. This study examines flexibility from both the technical and contractual angle, and their interactions, using the current context of Thailand’s power system. For technical flexibility, the report analyses the flexibility requirements and assesses the value of technical flexibility options, including flexible power plants, pumped storage hydro and battery energy storage systems. For contractual flexibility, the report analyses the impacts of existing power purchase agreement and fuel supply contract structures on system flexibility. This report provides recommendations for the system to be able to use the full range of flexibility options in the most cost-effective and secure way.