A process for preparing polybutylene terephthalate (PBT) which includes step of melting solid PBT oligomer having an IV of between 0.13 and 0.17 dL/g and a CEG of between 90 and 180 mmol/kg; and further step of the PBT oligomer polycondensation; wherein the polycondensation process is carried out continuously using a melt tank for melting oligomers, one or more reactors for post-condensation processing, and one or more finishing reactors to increase molecular weight. The resulting PBT has an intrinsic viscosity (IV) of between 0.5 and 1.3 dl/g and a carboxylic end group (CEG) concentration of between 1 and 75 mmol/kg.