The Trade Competition Act (TCA) seeks to maintain a fair and open market by prohibiting business operators from exerting unfair influence through monopoly, exclusivity, price fixing, quantity fixing, tying/bundling, etc. If any two business operators act together to effect such conduct, they may be liable for violating the TCA, which carries a prison term of up to three years and/or a fine of up to THB 6 million per violation. The TCA applies not only to any two or more business operators who are working together, but also to a single business operator acting alone if that single operator has “market dominance.” The market share requirements constituting “market dominance” are further explored in this article.