Disclosed are novel methods for embolizing blood vessels comprising delivering, via a catheter, an embolic composition comprising a biocompatible polymer, a biocompatible water insoluble contrast agent, and a biocompatible solvent. In one embodiment, the method is conducted during a single surgical procedure whereby a flow-arresting device is positioned and activated at the vascular site to be embolized, the embolic composition is injected, and the flow-arresting device is deactivated. In another embodiment, the method is conducted during a single surgical procedure whereby two embolic compositions, situated adjacent to one another, are injected at the vascular site to be embolized.