The poly(3-alkylthiophenes) are a class of electrically conducting polymers which are of particular scientific and commercial interest due to their solubility and meltabillty. A series of poly(3-octylthiophene) (P3OT) fractions having molecular weights in the range M(w) = 30,000 to 400,000 were generated by preparative gel permeation chromatography (GPC). Although the polymer remained weakly aggregated when dissolved in pure THF, the addition of an organic salt (1 wt.% tetrabutylammonium p-toluenesulfonate) resulted in complete molecular dissolution. We were thus able to completely and consistently describe the polymer’s single-chain properties using three dilute solution characterization methods : viscometry, GPC, and integrated light scattering. The molecular weight dependence of the intrinsic viscosity and the radius-of-gyration were established, and were characteristic of solutions near the theta condition, indicating poor solvent quality. Calculation of the persistence length from our data revealed that the polymer backbone is only 2 to 3 times more rigid than common flexible polymers, despite its conjugated ring structure.