Prof. Oki is a Special Advisor to the President, and a Professor at Graduate School of Engineering, The University of Tokyo. His previous academic positions include Associate Professor with the Institute of Industrial Science, The University of Tokyo and Associate Professor with the Research Institute for Humanity and Nature. He was also affiliated as the Senior Vice-Rector, United Nations University, Japan, and an Assistant Secretary-General, United Nations for 2016-2021.
His areas of expertise are global hydrology and the sustainability of world water resources including the virtual water trade and water footprint. He was one of the coordinating lead authors for the chapter "Freshwater Resources" of the IPCC WGII AR5. He got many awards such as the Biwako Prize for Ecology in 2011, and the Japan Academy Medal in 2008. He is the first Japanese AGU Fellow in its Hydrology Section (2014). He became a full member of the Club of Rome and the Science Council of Japan since October 2020; and received the 2021 International Hydrology Prize (Dooge medal) Winner.