To establish reliable numerical models that depict the geochemical processes caused by the storage of CO2 in saline aquifers it is essential to have an applicable database. This has to include thermodynamic properties and kinetic data of those gas mixtures occurring in the captured CO2 gas stream, which will contain minor amounts of gases such as O2, N2, NO x , SO x, CO, H2 S. However, quantitative measures of the chemical alterations due to these accessory gases are scarce at relevant conditions. The COORAL project “CO2 Purity for Capture and Storage”, concentrates on the effects of accessory gases during all four processes: capture, transport, injection and storage. At BGR it is the storage that is in focus. High-pressure-high-temperature (HPHT) experiments are carried out using unstirred batch- reactor systems (P & 590 bar; T & 350°C) to elucidate mineral and fluid alterations and quantify kinetic rates for different mineral–fluid–CO2–co-injected gas system. A first set of experiments using pure CO2 and carbonates allowed testing the laboratory set-up and adjusting the modelling environment (PHREEQC). Dolomite-brine-CO2 experiments exhibited a very good reproducibility of the increase in cation concentrations at the different stages of the experiment. Release rates for both, Mg and Ca, vary between 2*10-10 mol s-1 cm - 2 at the very beginning and 4*10-13 mol s-1 cm -2 just before approaching steady state. There is a tendency towards slightly higher rates for Ca release during the first stage of the experiment. The main target of the running experiments is set on the effects of binary gas mixtures in the system mineral–fluid–CO2–O2 (this contribution) and mineral–fluid–CO2–SO2 [1]. The mineral phase consists of carefully crushed, sorted and cleaned natural mono-minerals while the natural saline water is represented by a Na-Cl solution of 150 g/l NaCl in most cases.