Interference fringe fields and the visible flame field of a 50 mm diameter n-hexane tank flame were simultaneously measured using a real-time holographic interferometer with special image optics. An inhouse developed image processing method was applied to the holographic images to calculate the interference fringe order profiles. The effect of species composition on temperature profiles was studied by considering three different cases: using the measured species profiles, using an overall reaction mechanism based on stoichiometric combustion, and by assuming that the flame consists of hot air. The results show that species composition has the largest effect on temperature fields in regions near the flame axis at lower axial distances. In the region of the plume zone, the flame consists primarily of hot air due to the increase in total entrained air.