The effect of SiC concentration on the liquid and solid oxide phases formed during oxidation of ZrB2–SiC composites is investigated. Oxide-scale features called convection cells are formed from liquid and solid oxide reaction products upon oxidation of the ZrB2–SiC composites. These convection cells form in the outermost borosilicate oxide film of the oxide scale formed on the ZrB2–SiC during oxidation at high temperatures (≥1500°C). In this study, three ZrB2–SiC composites with different amounts of SiC were tested at 1550°C for various durations of time to study the effect of the SiC concentration particularly on the formation of the convection cell features. A calculated ternary phase diagram of a ZrO2–SiO2–B2O3 (BSZ) system was used for interpretation of the results. The convection cells formed during oxidation were fewer and less uniformly distributed for composites with a higher SiC concentration. This is because the convection cells are formed from ZrO2 precipitates from a BSZ oxide liquid that forms upon oxidation of the composite at 1550°C. Higher SiC-containing composites will have less dissolved ZrO2 because they have less B2O3, which results in a smaller amount of precipitated ZrO2 and consequently fewer convection cells.