The oxygen content of pulled silicon crystals, determined by vacuum fusion gas analysis, is correlated with the infrared absorption at 9 &mgr;. In vacuum and in helium or hydrogen of 1 atmos, the oxygen concentration of a liquid zone of silicon (about 20 mm2in cross section) can be rapidly decreased. In an oxygen atmosphere or in contact with quartz, liquid silicon picks up oxygen quite readily. A maximum oxygen content of 2×1018oxygen atoms per cm3was observed. Silicon single crystals pulled from a quartz crucible exhibit fluctuations in oxygen concentration both perpendicular and parallel to the pulling direction. Explanations of these effects are offered and the influence of various pulling parameters is discussed.