Topological superconductivity is an exotic phase of matter in which the fully gapped superconducting bulk hosts gapless Majorana surface states protected by topology. Intercalation of copper, strontium, or niobium between the quintuple layers of the topological insulator Bi2Se3 increases the carrier density and leads to superconductivity that is suggested to be topological. Here we study the electronic structure of strontium-intercalated Bi2Se3 using angle-resolved photoemission spectroscopy and Shubnikov-de Haas oscillations. Despite the apparent low Hall number of ∼2×1019cm-3, we show that the Fermi surface has the shape of an open cylinder with a larger carrier density of ∼1020cm-3. We suggest that superconductivity in intercalated Bi2Se3 emerges with the appearance of a quasi-Two-dimensional open Fermi surface.