This paper presents a detailed study of retention on a reversed-phase material made by coating potybutadiene (PBD) on porous zirconia. PBD-coated zirconia particles with six different carbon loads (0.25-5.6% carbon by weight) were prepared by evaporatively depositing and cross-linking PBD on microparticulate porous zirconia. Retention data of a homologous series of alkytbenzenes were obtained on the six PBD phases as a function of mobile phase composition in methanol-water and acetonitrile-water mixtures from 20 to 50% (v/v). The results obtained for the phase were compared to those for conventional octadecylsilane (ODS) bonded phases, and the effect of the amount of PBD on retention was studied in detail. We find that, per amount of bonded phase, the PBD phase is less retentive than is the ODS phase, but it has comparable Hydrophobic selectivity. Furthermore, the PBD phase has about the same sensitivity toward changes in mobile phase composition as does the ODS phase, and its solute shape selectivity is similar to that of a monomeric ODS phase. Finally, we conclude that retention arises primarily from a partition-like process.