A three chamber ultrahigh vacuum (UHV) surface analysis system combined with high pressure reaction cells has been designed. It can be used for the preparation and characterization of ordered metal oxide model catalyst surfaces and for the investigation of heterogeneous catalytic reactions there on also under high pressures. The reaction cells are completely separated from the UHV analysis chambers. They can be used for oxidation treatments and reaction studies at total pressures up to 1 bar. A new sample transfer mechanism together with sapphire sample holders and sample heating-cooling stations on the analysis chamber manipulators provides electron beam and resistive sample heating, liquid nitrogen sample cooling, and precise thermocouple temperature control. First experimental results obtained on single crystalline iron oxide dehydrogenation films grown onto Pt(lll) substrates are presented. These results demonstrate the capability of the system for in situ investigation of a sample surface using scanning tunneling microscopy, low-energy electron diffraction, Auger electron spectroscopy, photoelectron emission microscopy, and temperature programmed desorption before and after catalytic reactions at high pressures. This single crystal surface science approach provides new insight into the atomic scale surface chemistry of metal oxides under real catalysis conditions.