Modelling of the flame displacement speed is of interest in many Large Eddy Simulation (LES) frameworks including the Flame Surface Density approach. In this study, a Direct Numerical Simulation (DNS) dataset is used to calculate the displacement speed in a premixed, methane–air, round jet flame in the thin reaction zone (TRZ) regime. Three progress variables are used, defined with the mass fractions of selected reactant and product species and with the sensible enthalpy of the mixture. Analysis of the conditional statistics shows that the density weighted displacement speed S d at a given iso-surface of the progress variable c differs from the laminar flame speed, particularly close to the flame tip. In addition, the contribution of tangential diffusion to the changes of S d does not fully explain the observed deviation. It is also shown that different definitions of c lead to different results for S d as a function of c, thereby highlighting the impact of the chosen progress variable on the variations of flame displacement speed.