Poly(3-octylthienylene vinylene) (o-ptv) has a great potential as low-bandgap p-type semiconductor for photovoltaic applications. Here, the positive radical state (positive polaron) is induced chemically in the o-ptv polymer in which the vinylene sites are selectively 13c-labeled. Using multi-frequency continuous wave and pulsed electron paramagnetic resonance, the g tensor and maximum 1h and 13c hyperfine couplings are determined. A comparative density functional theory (dft) analysis of ptv-like oligomers is performed. The experimental parameters suggest a larger localization of the positive polaron than follows from the dft analysis. The counter anion may play a crucial role in localizing the polaron.