Abstract: Methods for quantifying, in near real-time, the amount of silicon oxide (SiO) volatilized from a pool of molten silicon such as a Czochralski silicon melt and present in the atmosphere over the melt are disclosed. A preferred method includes reacting a gas sample containing SiO withdrawn from the atmosphere over the molten silicon with a reactant to form a detectable reaction product, determining the amount of reaction product formed, and correlating the determined amount of reaction product to the amount of SiO present in the atmosphere. The quantification of SiO is used for monitoring and/or controlling the amount of oxygen in the molten silicon or the oxygen content in single crystal silicon being drawn from the molten silicon. A SiO reaction probe and a system using the probe for monitoring and/or controlling oxygen are also disclosed.