In 1935 and 1936 he further explored the Fezzan, from both the geological and hydrological point of view, and the Tibesti massif in the Central Sahara. From 1936 to 1940, he organized and directed the Libyan Geological Survey, which included research into mining and artesian waters by order of the Government of Libya. Desio discovered in 1938 natural oil in the subsurface of Libya.