Thailand’s Energy Regulatory Commission (ERC) has issued four new regulations under the Energy Business Act B.E. 2550 (2007) setting forth competition regimes to control both anticompetitive conduct and market structure in the energy business sector. The regulations were published in the Government Gazette on December 19, 2022, and took effect the following day. The key provisions of these ERC competition regulations largely mirror those articulated in the Trade Competition Act B.E. 2560 (2017) and its subordinate legislation. The most significant features of these competition regulations are summarized below. Market Definition Regulation The ERC’s market definition regulation (officially the ERC Regulation re: Market Definition and Relevant Market of Related Energy Services B.E. 2565) outlines the general framework for defining relevant markets in the energy sector. The factors to be taken into consideration include types of energy licenses, geographical areas, competition conditions, and interchangeability of energy services. In the annex to this regulation, the ERC has classified the relevant energy service markets as follows: Power business activities include power generation, power transmission system services, power distribution system services, power distribution services, and power system control services. Natural gas business activities include natural gas transmission through pipelines via natural gas transmission systems, natural gas procurement and wholesale via natural gas distribution systems, natural gas retail via natural gas distribution systems, and storage and regasification of liquefied natural gas. The ERC will review its market definitions and relevant energy service markets from time to time, taking into account changes in technology and competition conditions as well as feedback from public hearings. Market Dominance Regulation Under the ERC’s market dominance regulation (officially the ERC Regulation re: Criteria on Business Operator having a Market Dominance B.E. 2565), the ERC is empowered to proactively determine and declare which license-holding energy business operators have a dominant position