Organised and led the expedition on the balsa raft Kon-Tiki from Peru to Polynesia in 1947 to prove the possibility of aboriginal South American voyages to the Oceanic islands. Organised and led Norwegian Archaeological Expedition to the Galapagos Islands revealing evidence of pre-historic camp sites and experimenting with aboriginal tacking principles of balsa raft in Ecuador 1952-53. Organised and led Norwegian Archaeological Expedition to Easter Island and the East Pacific discovering distinct cultural layers with South American correspondences, thus introducing stratified archaeology to East Polynesia 1955-56.

Continued research on Polynesian culture and migrations 1957-68. The earlier research on Pacific migration routes was expanded to a more global interest in cultural origins, navigation and trans-oceanic contacts, once the Easter Islanders had demonstrated the seaworthiness of the Peruvian-type totora reed ship. Began experiments with the seaworthiness of reed ships 1969 sailing the totora ship Ra II with an international crew from Safi, in Morocco, to Barbados in 1970. Continued research on pre-European navigation until sailing the Sumerian-type reed ship Tigris with an international crew of eleven men from Qurna in Iraq by way of the Indus Valley to Djibouti in Africa 1977-78. Organised and led Kon-Tiki Museum Archaeological Expeditions to Maldive Islands discovering Buddhist and Hindu temple ruins preceding the 12th century Muslim settlement, 1982-84.

Organised Norwegian-Chilean Archaeological Expeditions to Easter Island excavating further pre-Inca walls and conducting the first experiments in moving statues in an up-right position, 1986-88. Since 1990 also established a Norwegian-Spanish archaeological project in the Canary Islands, protecting the newly identified step-pyramids in Güímar on Tenerife.

In 2001 organised the joint Russian-Norwegian archaeological expedition to Azov in the delta of the river Don, which revealed that this old fortified town was an extremely important trading centre in Antiquity.