An optical absorption band at 9\ensuremath{\mu} has been correlated with the oxygen content in silicon. Pulled silicon crystals were found to contain up to ${10}^{18}$ oxygen atoms per ${\mathrm{cm}}^{3}$ which seem to originate from the quartz crucible. The oxygen concentration in silicon crystals prepared by the floating zone technique in vacuum was found to be less than ${10}^{16}$ oxygen atoms per ${\mathrm{cm}}^{3}$. The 9\ensuremath{\mu} absorption due to silicon-oxygen bond stretching vibrations provides a possibility for a quantitative oxygen analysis of high sensitivity. A corresponding absorption in germanium at 11.6\ensuremath{\mu} is believed to be due to a germanium-oxygen vibration.