Mycobacterium PYR-1 was used in a two-phase partitioning bioreactor (TPPB) to degrade low and high molecular weight polycyclic aromatic hydrocarbons. TPPBs are characterized by a cell-containing aqueous phase, and an immiscible and biocompatible organic phase that partitions toxic substrates to the cells based on their metabolic demand and the thermodynamic equilibrium of the system. A bioavailable solvent, that is, a solvent usable as a carbon source, was used as the organic layer. Although bioavailable solvents are traditionally deemed unsuitable for use in TPPBs, bis(ethylhexyl) sebacate had superior chemical properties to other solvents examined and was cost-effective. In this system, 1 g of phenanthrene and 1 g of pyrene were completely degraded within 4 days, at rates of 168 mg l(-1) day(-1) and 138 mg l(-1) day(-1), respectively, based on a 3-1 aqueous volume. This is the highest pyrene degradation rate reported in the literature to date. Significant degradation of naphthalene and anthracene was also obtained. This work demonstrates that bioavailable solvents can be successfully used in TPPB systems, and may change the protocols commonly used to select solvents for TPPBs in the future.