To reduce CO2 emissions into the atmosphere, different scenarios are proposed to capture and store carbon dioxide (CO2) in geological formations (CCS). Storage strategies include CO2 injection into deep saline aquifers, depleted gas and oil reservoirs, and unmineable coal seams. To identify a secure and proper strategy for CO2 injection, the fluid displacement at reservoir conditions and thus the wettability of the geological formation need to be understood. Wettability has a strong effect on multiphase rock-fluid interactions and influences the efficiency of an immiscible displacement in the porous medium, the magnitude of irreducible water and residual oil saturations, the microscopic fluid distribution at pore scale in the porous medium, the capillary pressure and relative permeability curves and the electrical properties of the porous medium. Only a limited amount of literature refers to wetting properties of sedimentary rocks and minerals at high pressures and elevated temperatures. Hence, a reliable experimental method to determine the wettability is an important step towards understanding the physics of this phenomenon. This thesis is a collection of experimental work on rock-fluid interactions and wettability behavior of the rock surface related to CO2 storage. The captive-bubble technique is used to evaluate the wetting properties of different rock surfaces in the presence of CO2 and/or synthetic flue gas. To mimic the in-situ conditions, experiments are performed at high pressures and elevated temperature (up to 16 MPa and at 318 K).