The present invention relates to biocompatible oligomer-polymer compositions for the in situ formation of implants, wherein the implants release a bioactive agent, a metabolite, or a prodrug thereof, at a controlled rate. The sustained release delivery system includes a flowable composition containing a bioactive agent, a metabolite, or a prodrug thereof, and an implant containing a bioactive agent, a metabolite, or a prodrug thereof. The flowable composition may be injected into tissue whereupon it coagulates to become the solid or gel, monolithic implant. The flowable composition includes a biodegradable, thermoplastic polymer, a biocompatible end-capped oligomeric liquid, and a bioactive agent, a metabolite, or a prodrug thereof.
