Abstract In a context where the aviation sector is actively looking into replacing standard jet fuels with sustainable aviation fuels (SAFs), examining the effects of fuel composition on combustion dynamics is of current interest. There are indeed indications that the chemical composition may notably impact the location of the unstable operating points and the amplitude and frequency of thermo-acoustic oscillations. The fuel composition effect is hence investigated in this article by considering the case of binary fuel mixtures composed of heptane and dodecane, two fuels presenting very different volatilities (Tboil = 380 K for heptane and Tboil = 480 K for dodecane). The blends composition is varied between pure heptane and pure dodecane, and the corresponding dynamical behavior is observed in an annular combustor equipped with swirl spray injectors. It is shown that the composition changes the location, extent, and geometry of the unstable domain. The frequency of the instability also depends on fuel composition. The differences in behavior observed for the different blends are then characterized by measuring flame describing functions (FDFs). These functions are determined in a separate burner representing a sector of the annular chamber in which the air flow is modulated from the upstream side. It is found that the FDF gain and phase curves change with the fuel blend. These data, combined with a reduced-order thermo-acoustic model, are used to interpret the experimental observations. From a more practical standpoint, this study indicates that it is important to examine the dynamical behavior of combustors that will use novel fuels like SAFs.