We present high temperature investigations on ferrosilicon alloys (Si: 24.7, 74, and 98.5%); silicon oxidation and decarburization studies in steelmaking have generally been limited to Fe-based alloys containing up to 3.5 wt% Si. The effect of alloy composition, oxygen partial pressure and gas flow rate on interactions at 1823 K is evaluated. Decarburization and silicon oxidation reactions were found to occur simultaneously with significant differences observed in the weight gain and carbon loss. The net weight gain in these alloys was found to be due to the combined influence of decarburization (weight loss due to the generation of a gaseous product) and silicon oxidation (weight gain due to silica formation on the sample surface). There was a clear evidence for two rate regimes: the rate of decarburization was found to be much higher during the initial 2 min and a much slower rate was observed in later stages for all specimens. These rate regimes are explained in terms of the extent of surface coverage with the reaction product silica. No significant effect was found on the decarburization rates when the proportion of oxidizing gas (CO2) was increased from 20 to 100%. The outcomes of this investigation will assist with the development of mechanisms governing the reactions of molten ferrosilicon and silicon alloys during their interactions with gaseous phases in the cupola process.