Polyethyleneglycol (PEG) dialkyloxypropyl (DAA) lipid conjugates having the structure of formula (I) are disclosed, wherein R1 and R2 are independently selected and are alkyl groups having from about 10 to about 20 carbon atoms PEG is a polyethyleneglycol, wherein the terminal hydroxyl group is substituted with a methyl group and L is a non-ester containing linker moiety, wherein said non-ester containing linker moiety is a member selected from an amido linker moiety, an amino linker moiety, a carbonyl linker moiety, a urea linker moiety, an ether linker moiety, a disulphide linker moiety, a succinamidyl linker moiety and combinations thereof. These compounds have an increased stability over commonly used PEG-lipids conjuguates. Liposomal compositions, stabilized plasmid-lipid particles (SPLP) and stabilized nucleic acid-lipid particles (SNALP) comprising said PEG-DAA conjuguates, for delivery of a bioactive agent to a cell or patient are also described.
