Poly(ester-anhydrides) or polyesters formed from ricinoleic acid and natural fatty diacids and their method of preparation and its use for delivering bioactive agents including small drug molecules, peptides and proteins, DNA and DNA complexes with cationic lipids or polymers or nano and microparticles loaded with bioactive agents are disclosed herein. The drug delivery compositions are administered to a patient in a liquid form, increase in viscosity in vivo to form a drug depot or implant, and are able to release the incorporated bioactive agent for weeks. In the preferred embodiment, the drug delivery formulations are administered by injection. In one embodiment, the compositions are suitable for local or regional delivery of drugs to diseased sites, such as treating solid tumors and bone infections. In a preferred embodiment, the drug delivery compositions are suitable for site-specific chemotherapy for the treatment of solid tumors including: squamous cell carcinoma (SCC) of the head and neck, prostate cancer, and sarcomas for intratumoral injection or insertion.