Academician Mikhail Dmitrievich Millionshchikov was an outstanding Russian scientist and organiser of science. An alumnus of the Grozny Oil Institute, he was engaged in the issues of oil production in the beginning of his scientific career. In the 1930s, he shifted his attention to the problems in the theory of turbulence (his works in this field garnered him both the national and the international recognition) but later returned to the theme of oil production, which was reflected in his Thesis for the Doctor of Sciences degree. The history of the defence of his thesis has not been covered in the history-of-science literature so far and this paper is devoted to this little-known part of Millionshchikov’s scientific biography.