For the first time, the charge states of adsorbed oxygen adatoms on rutile TiO2(110)-1×1 surface are successfully measured and deliberately manipulated by a combination of noncontact atomic force microscopy and Kelvin probe force microscopy at 78 K in ultrahigh vacuum and interpreted by extensive density functional theory modeling. Several kinds of single and double oxygen adatom species are clearly distinguished and assigned to three different charge states: Oad-/2Oad-, Oad2-/2Oad2- and Oad--Oad2-, i.e. to formal charges of either one or two electrons per atom. Due to the strong atomic-scale image contrast, these states are clearly resolved. The observations are supported by measurements of the short-range force and local contact potential difference as a function of tip-sample distance, as well as simulations. Comparison with the simulations suggests subatomic resolution by allowing to resolve the rotated oxygen p orbitals. In addition, we manage to switch reversibly the charge states of the oxygen adatoms, between the Oad- and Oad2- states, both individually and next to another oxygen, by modulating the frequency shift at constant positive voltage during both charging and discharging processes, i.e. by the tip-induced electric field of one orientation. This work provides a novel route for the investigation of the charge state of the adsorbates and opens up novel prospects for studying transition metal oxide based catalytic reactions.