Experiments on combustion of heptane/hexadecane mixture droplets were conducted in a reduced-gravity environment. Initial droplet diameters ranged from 0.47 to 1.5 mm, and initial hexadecane mass fractions ranged from 0.05 to 0.4. The ambient gas was O-2/He (with O-2 mole fractions of 0.3 and 0.5), or atmospheric air, and pressures were varied from 0.033 to 0.3 MPa tabs). A previous asymptotic theory was extended to allow data on flame contractions to be used to estimate liquid species diffusion coefficients. The liquid species diffusion coefficients were found to vary significantly with pressure; this is attributed to variations in droplet temperatures.