A liposome suspension forms spontaneously upon adding a lipid composition to an aqueous solution. The liposomes include diacylglycerol-PEG compounds. The melting point of the diacylglycerol-PEG is below about 40 degrees C., and the acyl chains of the diacylglycerol-PEG are greater than or equal to 14 carbons in length. Such liposome suspensions are useful for a variety of purposes, including the delivery of therapeutic agents.