Injectable depot compositions are provided that include a polymer matrix having a plurality of bioerodible, biocompatible polymers wherein each polymer of the plurality of polymers has a specified average molecular weight, and the polymer matrix has a broad molecular weight distribution of the plurality of polymers; a solvent having a miscibility in water of less than or equal to 7 wt % at 25° C., in an amount effective to plasticize the polymer and form a gel therewith; and a beneficial agent. The compositions have substantially improved shear thinning behavior and reduced injection force, rendering the compositions readily implanted beneath a patient's body surface by injection.