In this study, the liquid viscosity and interfacial tension of binary and ternary mixtures containing n-octacosane (n-C28H58) and different byproducts typically found in the Fischer-Tropsch process were investigated. For the binary mixtures having mole fractions of the byproducts between 0.02 and 0.40, the effects of varying branching, alkyl chain length, and degree of oxygenation in selected byproducts on viscosity and interfacial tension were studied. In detail, the isomers n-decane, 2-methylnonane, and 4-methylnonane were used to study differences in branching for alkanes with the same molecular weight. The 1-alcohols ethanol and 1-dodecanol as well as the carboxylic acids formic acid and acetic acid imply variations in the alkyl chain length and degree of oxygenation. In addition, two ternary systems consisting of n-octacosane, n-decane, and ethanol with mole fractions of 0.6 of either n-alkane and 0.2 for each of the other two components were selected. On the basis of the surface light scattering (SLS) method analyzing microscopic surface fluctuations at macroscopic thermodynamic equilibrium, the liquid viscosity and interfacial tension of the studied mixtures could be determined at saturation conditions at temperatures from (373.15 up to 523.15) K with average expanded measurement uncertainties (k = 2) of (2.7 and 2.4)%. Except for systems containing the two branched alkanes showing a distinct decrease in the interfacial tension even at low mole fractions of 0.025, liquid viscosity and interfacial tension at 423 K are not strongly affected with increasing concentration of the byproducts up to 0.10 compared to the values for pure n-octacosane within relative deviations of 10% and 5%. For the studied binary and ternary systems, simple mixing rules for liquid viscosity and interfacial tension based on the corresponding properties of the pure components are discussed.