Weak satellites in S-1<--S-0 excitation spectra of natural-abundance pentacene in p-terphenyl due to position-specific C-13 isotope shifts were observed. An assignment of these satellites to the various carbon positions is derived. The extremely narrow inhomogeneous linewidth allowed selective excitation of pentacene molecules with C-13 in specific positions. Spectra of the magnetic-resonance transition between triplet sublevels of such ensembles, and of individual pentacene molecules showed position-specific C-13 hyperfine broadening.