Indonesia-Singapore border

The Indonesia–Singapore border is a maritime boundary in the Straits of Singapore between Indonesia's Riau Islands which lie to the south of the border, and the islands of Singapore which lie to the north. The Straits of Singapore is one of the region's busiest waterways as it is the main channel for Singapore's ports.

Only a portion of the maritime border between the two countries has been determined. The remaining parts, especially those lying to the east of the delimited boundary, may require the involvement of Malaysia as the country also possesses territorial waters in the area.

The Agreement Stipulating the Territorial Sea Boundary Lines between Indonesia and the Republic of Singapore in the Strait of Singapore signed by Indonesia and Singapore on 25 May 1973 determines the common territorial sea border as a series of straight lines connecting six coordinate points located in the Straits of Singapore. Indonesia ratified the agreement on 3 December 1973 while Singapore ratified the agreement on 29 August 1974.

The distance of the border is 24.55 nautical miles (45.47 km). Three of the six coordinates lie equidistant from Indonesian and Singaporean shores while the remaining are negotiated points with two lying closer to the Indonesian shores. Point 2 lies towards the landward side of Indonesia's baseline.

On 10 March 2009, Indonesia and Singapore signed the Treaty between the Republic of Indonesia and the Republic of Singapore Relating to the Delimitation of the Territorial Seas of the Two Countries in the Western Part of the Strait of Singapore 2009 in Jakarta. The treaty, signed by their respective Foreign Ministers at that time, namely Hassan Wirajuda and George Yeo, extended the delimitation of their common maritime boundary by a further 12.1 km westwards from Point 1 determined in the 1973 agreement, to Point 1C. The treaty came into force upon ratification through an exchange of Instruments of Ratification on 31 August 2010 in Singapore by then Indonesian Foreign Minister Marty Natalegawa and his Singaporean counterpart George Yeo.

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