The solubilities of three P3HT samples of similar regioregularity (rr ≈ 96%) but varying molecular weight (M n = 14 kDa, 32 kDa, and 49 kDa) are measured in 23 organic solvents. The solubility data is used to calculate the partial solubility parameters (δ D , δ P , δ H ) using the functional solubility parameter (FSP) method.The results reveal a monotonic decrease in the polar and hydrogen-bonding parameters, δ P and δ H , respectively, with increasing molecular weight of the polymer. The observed trends are consistent with recent experimental and computational results and are rationalized in terms of increasing torsional and conformational disorder of higher molecular weight P3HT following dissolution in solvents of decreasing P3HT solubility. The results indicate that the structural attributes of the P3HT chains in the solutions impact the nature and strength of the polymer-solvent interactions, and that these structural effects are registered by the observed solubility parameters.