High-pressure CO adsorption on Pd(111) was examined by X-ray photoelectron spectroscopy (XPS) and vibrational sum frequency generation (SFG) from 200 to 400 K, and in a pressure range from 10(-6) to 1 mbar. Even in the millibar regime both methods indicated that CO adsorbed in "regular" adsorption sites such as hollow, bridge, and on-top. By combination of XPS and SFG, a quantitative analysis of CO coverages at various pressures was performed. At high pressure, no CO structures different from those known from UHV studies were observed. Also, no indications of CO dissociation or carbonyl formation were found under the given experimental conditions, provided that the CO gas was sufficiently cleaned.