This retrospect traces the development of commercial mass spectrometers for use in the petroleum industry, starting with the formation of Consolidated Engineering Corporation in 1937 and installation of their first instruments in 1942 and 1943. During the middle and late forties, just keeping the machines running placed major demands on the time, energy and ingenuity of mass spectrometrists. The fifties saw progressive exploration of the chemical basis of mass spectra, culminating in the Eighth Annual Meeting of ASTM Committee E-14 on Mass Spectrometry in 1960. This meeting marked a turning point in the development of the field—its transformation from what was originally almost a cult to a widely accepted and recognized branch of physical organic chemistry.