Prefilled syringes are often used for packaging and delivery of therapeutic proteins. But the silicone oil lubricant can cause protein aggregation and promote adverse immunogenicity. In this presentation, data on these two topics will be summarized. In addition, the mechanism for silicone oil-induced protein aggregation will described, and formulation approaches to mitigate protein aggregation will be highlighted. Finally, the problems of analyzing samples that contain both protein particles and silicone oil droplets, and the solutions to these problems afforded by the unique data available from the Archimedes instrument, will be addressed.