Ceremonial exchange systems serve political purposes, economic purposes, or both. Systems operating in the highlands include moka (the exchange of pigs and shells in the Western Highlands), mok-ink (pig exchange in the Southern Highlands) and te (pig exchange in Enga). Coastal and island exchange systems include hiri and kula. Although the importance of such exchanges diminished when people came into contact with Western society and traditional social and economic relationships became less important, the highlands pig exchange systems and the kulastill operate.
Until World War II a major annual Papuan trading expedition in which pots were exchanged for sago. Each October or November, Motu men took pots, made by the women, several hundred kilometers northwest across the Gulf of Papua. They returned with sago each December or January. These expeditions were made in large double canoes which took advantage of the prevailing winds. The exchanges served social as well as economic purposes. Both sago and pots became articles of trade in other networks. The Motu, for example, traded sago both to inland villages and to coastal villages to the southeast. Sago provided food during a seasonal “time of hunger”. The scale of the trade was considerable. One observer in the first decade of the 20th century noted that the hiri fleet consisted of some 20 canoes, that the fleet carried more than 25,000 pots to the northwest each year, and that each canoe returned with about 25 tons of sago. Before metal tools of European manufacture became available during the 19th century the hiri also carried stone axes to the Gulf coast where stone suitable for axe-making was not available. The Motu obtained the stone axes from inland villages.
The kula ring is an exchange system of the islands lying to the southeast of the mainland of PNG. The system serves both ceremonial and trade purposes and has probably been operating for some thousands of years. Highly valued red shell necklaces travel clockwise and white shell armbands travel counter-clockwise twice yearly. Items traded during the kula visits include food, stone for tools and pottery. This cycle, which was studied, and described in great detail, by the anthropologist Bronislaw Malinowski, was one of a number of ceremonial and trading patterns which operated in PNG. The kula gradually declined in importance in the 19th century but some items were still in circulation in the early 1990s.