Oil-containing particles with a single depression were created by polymerization to form polymeric shells encapsulating oil droplets of polydimethylsiloxane (PDMS) that were prepared by the base-catalyzed hydrolysis and condensation of dimethyldiethoxysilane (DMDES). A reactive silane agent of 3-methacryloxypropyltrimethoxysilane (MPTMS) was added to the PDMS emulsion and used as a source of the polymeric shell. The water-soluble initiator potassium persulfate was employed to initiate the polymerization for the shell formation. Polymeric particles with a wrinkled depression were observed at low MPTMS concentrations, whereas those with a pseudo-hemispherical depression were obtained at high MPMTS concentrations. Another shell source, styrene (St), was added to the polymerization system for extending morphologies of the oil-containing particles. An increase in MPTMS concentration in the polymerization with the addition of St varied the depression shape from an ellipsoidal hemisphere to a pseudo-hemisphere. Spherical particles without any depression were also obtained at a high MPTMS concentration in the polymerization with the addition of St. The containment of PDMS oil in the polymeric particles was confirmed by thermal gravimetric analysis (TGA) and energy dispersive X-ray (EDX) measurement. Shrinkage volumes by the polymerization of MPTMS and St were calculated to examine the dominant factor for formation of the depression. The calculation of shrinkage volumes indicated that the volume shrinkage of MPTMS in the polymerization was an important factor to determine the morphology of oil-containing particles.