[4] 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.

In retirement, he remained active as an occasional lecturer, a journal editor, and a translator of scientific books and articles.

His scientific accomplishments at this stage of his career included demonstrating the utility of the compound ferrous ethylene diamine sulfate in certain applications especially redox titrations.

[5][6] A further contribution to analytical chemistry was his demonstration of the use of naphthidine as an indicator for certain chromate titrations such as for chloride ion.

[6] Oesper wrote numerous short biographies of notable chemists and lectured on the history of chemistry.

[9] In 1954, Oesper received the 5th annual Eminent Chemist award by the American Chemical Society.

[4] In 1956 he received the first Dexter Award for Outstanding Achievement in the History of Chemistry from the American Chemical Society.

[3] Oesper was a member of the editorial boards of the Journal of Chemical Education, Chymia, Mikrochemie, and Microchimica Acta.