The maritime boundary between India’s Nicobar Islands and Thailand’s Simlan Islands is based on the principle of equidistance and extends from a tripoint with Indonesia in the south to a tripoint with Myanmar in the north. The boundary goes in a north – south direction through the southern Andaman Sea for approximately 115 nautical miles.

India and Thailand reached this boundary agreement on 22 June 1978, and it was immediately followed by a tripoint agreement with Indonesia later that same day. The agreement on the northern tripoint with Myanmar was finally reached on 27 October 1993.