The pressure p-temperature T projections of solid-liquid-gas (S-L-G) three-phase coexistence lines for the carbon dioxide + octadecanoic acid (stearic acid; C(18)H(36)O(2)) system and the carbon dioxide + 1-octadecanol (stearyl alcohol; C(18)H(38)O) System were measured by the first melting point method in which the initial appearance of the liquid phase was observed. The experimental p-T projections of the S-L-G lines were also correlated by the Peng-Robinson equation of state and the van der Waals type mixing rules with two binary interaction parameters introduced into attraction term and size terms, respectively. The present model gave good correlation results for all of the experimental S-L-G lines with maximum average absolute relative deviations of 0.32 % for the carbon dioxide + octadecanoic acid system and 0.32 % for the carbon dioxide + 1-octadecanol system.