The influence of heavy linear alkanes concentration on the wax crystallization tendency or wax appearance temperature (WAT) of a paraffinic crude oil and on a paraffin inhibitor effectiveness was evaluated by means of polarized light microscopy. A crude oil insensitive to the addition of wax inhibitors was fractionated into its hydrocarbon class fractions. Virgin crude oil distillation, deasphaltation of the 385 degrees C+ residue, HPLC separation of the heavy saturated hydrocarbons, and molecular sieves adduction enabled us to isolate the linear paraffins fraction with a carbon distribution of more than 24 atoms (nC24+- paraffins). A synthetic crude was prepared by mixing all separated fractions, except nC24+ paraffins, and the effect of this fraction concentration was evaluated by its controlled addition to the synthetic crude followed by cloud point measurements of all doped samples. The influence of this hydrocarbon class family concentration on a maleic anhydride copolymer derivative paraffin inhibitor (MAC) efficiency was also evaluated in all doped synthetic crudes. Abundance of these large linear alkanes increases the crude oil tendency to wax crystallization, a fact that was demonstrated by a linear correlation between the concentration of this hydrocarbon family and the crude oil cloud point. nC24+ paraffins proved to be deleterious for the efficiency of the selected paraffin inhibitor, affording an asymptotic curve which tends to a zero activity value at 30 wt % concentration of this fraction. Additionally, it was demonstrated that the flocculated asphaltenes provide wax crystallization sites whose presence increases the cloud point of the crude oil and also interferes with the crystal inhibition mechanism.