Gunnar Hansen Horn (25 June 1894 – 15 July 1946) was a Norwegian petroleum geologist and Arctic explorer. He is most renowned as the leader of the Bratvaag Expedition that found the long-lost remains of S. A. Andrée's Arctic balloon expedition of 1897 at Kvitøya in 1930.
Horn studied mining at the Norwegian Institute of Technology, graduating in 1916. He then studied petroleum geology at London's Royal School of Mines, and took a PhD in coal petrography at the Berlin Technical University. He was the leading Norwegian authority on coal and petroleum geology in the interwar years. He worked from 1920 to 1923 as a petroleum geologist in Trinidad and Venezuela. In the autumn of 1925, Horn travelled with Johan Braastad to the eastern shores of the Caspian Sea to investigate local oil resources.
After returning from Trinidad, he worked on Norway's Svalbard and Arctic Ocean Surveys. That included investigating and analyses all the most important coal measures on Svalbard. He also studied karst topography. In addition to his purely scientific work, Horn also had important practical and administrative duties in the Arctic islands.
During 1930, he headed an expedition with the sealer Bratvaag which found the camp of Swedish Arctic scientist Salomon August Andrée on Kvitøya. Other expeditions went to East Greenland and Franz Josef Land.