The Tapi (or Tapee) river (Thai: แม่น้ำตาปี, rtgs: Maenam Tapi, Thai pronunciation: [mɛ̂ːnáːm tāːpīː]) is the longest river in southern Thailand. The river originates at the Khao Luang mountain in Nakhon Si Thammarat Province, and has a wide estuary into the Gulf of Thailand at Bandon Bay near the town of Surat Thani.