Equilibrium passive samplers are promising tools to determine freely dissolved aqueous concentrations (C(W,free)) of hydrophobic organic compounds. Their use in the field, however, remains a challenge. In the present study on native polycyclic aromatic hydrocarbons (PAHs) in Oslo Harbor, Norway, two different passive sampler materials, polyoxymethylene (POM; thickness, 55 microm [POM-55] and 500 microm [POM-500]) and polydimethylsiloxane (PDMS; thickness, 200 microm), were used to determine in the laboratory C(W,free) in sediment pore water (C(PW,free)), and the suitability of five passive samplers for determination of C(W,free) in overlying surface water was tested under field conditions. For laboratory determinations of C(PW,free), both POM-55 and PDMS turned out to be suitable. In the field, the shortest equilibrium times (approximately one month) were observed for POM-55 and PDMS (thickness, 28 microm) coatings on solid-phase microextraction fibers, with PDMS tubing as a good alternative. Low-density polyethylene (thickness, 100 microm) and POM-500 did not reach equilibrium within 119 d in the field. Realistic values were obtained for dissolved organic carbon-water partition coefficients in the field (approximately one log unit under log K(OW)), which strengthened the conclusion that equilibrium was established in field-exposed passive samplers. At all four stations, chemical activity ratios between pore water and overlying water were greater than one for all PAHs, indicating that the sediment was a PAH diffusion source and that sediment remediation may be an appropriate treatment for PAH contamination in Oslo Harbor.