A two-dimensional electron gas (2DEG) in SrTiO3is created via modulation doping by interfacing undoped SrTiO3with a wider-band-gap material, SrTi1xZrxO3, which is doped n-type with La. All layers are grown using hybrid molecular beam epitaxy. Using magnetoresistance measurements, we show that electrons are transferred into the SrTiO3, and a 2DEG is formed. In particular, Shubnikov-de Haas oscillations are shown to depend only on the perpendicular magnetic field. Experimental Shubnikov-de Haas oscillations are compared with calculations that assume multiple occupied subbands.