The influence of gaseous fuel type and load on flame characteristics was experimentally investigated in a 1.3 MWth reheating furnace burner. In this study, LNG, LPG, and LPG/Air were selected as fuel, and fuel loads were set to 15%, 30%, and 60% in order to study gas interchangeability. The experimental results showed that the fuel change shows minor effect on the flame appearance for different fuel load conditions. The flame straightness performance was degraded under 30% fuel load conditions. The flame straightness performance was improved by injection of the burner center air. Minimum 10% air was required to improve the flame straightness performance compared to without burner center air conditions.