Following completion of his PhD degree, Oesper taught for a brief time at New York University and then at Smith College as a non-tenure track faculty member. He then in 1918 became a tenure track faculty member and later a full professor at the University of Cincinnati, where he remained until his retirement in 1951 as professor emeritus. In retirement, he remained active as an occasional lecturer, a journal editor, and a translator of scientific books and articles.
Oesper wrote approximately 300 scientific articles on analytical and organic chemistry, colloid chemistry and chemical history. He was fluent in the German language and translated about 20 chemistry books and numerous articles from German into English. He also translated chemistry articles from French and Dutch into English.