A Bilateral Monopoly (BIM) is a market structure that exists when a market has only one supplier and one buyer.

Reference Definition by IGU: A Bilateral Monopoly (BIM) is a type of LNG price formation mechanism. The BIM price is determined by bilateral discussions and agreements between a large seller and a large buyer, with the price being fixed for a period of time – typically one year. There may be a written contract in place but often the arrangement is at the Government or state-owned company level. Typically, there would be a single dominant buyer or seller on at least one side of the transaction, to distinguish this category from GOG, where there would be multiple buyers and sellers trading bilaterally.