The present invention relates to compositions forming a low viscosity mixture of: a) 20-80 wt. % of at least one diacyl glycerol and/or a tocopherol; b) 20-80 wt. % of at least one phosphatidyl choline (PC); c) 5-20 wt. % of at least one biocompatible, organic mono-alcoholic solvent; d) up to 20 wt. % polar solvent e) at least one peptide active agent; f) optionally at least one antioxidant; wherein the ratio of components a:b is in the range 40:60 to 54:46; wherein the pre-formulation forms, or is capable of forming, at least one liquid crystalline phase structure upon contact with excess aqueous fluid. The invention further relates to methods of treatment comprising administration of such compositions, and to pre-filled administration devices and kits containing the formulations.