The atomic-scale properties of lanthanum–strontium manganite (La_1−xSr_xMnO_3−δ, LSMO) surfaces are of high interest because of the roles of the material as a prototypical complex oxide, in the fabrication of spintronic devices and in catalytic applications. This work combines pulsed laser deposition (PLD) with atomically resolved scanning tunneling microscopy (STM) and surface analysis techniques (low-energy electron diffraction – LEED, X-ray photoelectron spectroscopy – XPS, and low-energy He⁺ ion scattering – LEIS) to assess the atomic properties of La_0.8Sr_0.2MnO₃(110) surfaces and their dependence on the surface composition. Epitaxial films with 130 nm thickness were grown on Nb-doped SrTiO₃(110) and their near-surface stoichiometry was adjusted by depositing La and Mn in sub-monolayer amounts, quantified with a movable quartz-crystal microbalance. The resulting surfaces were equilibrated at 700 °C under 0.2 mbar O₂, i.e., under conditions that bridge the gap between ultra-high vacuum and the operating conditions of high-temperature solid-oxide fuel cells, where LSMO is used as the cathode. The atomic details of various composition-related surface phases have been unveiled. The phases are characterized by distinct structural and electronic properties and vary in their ability to accommodate deposited cations.