The precise and detailed chemical shift of gas-phase hydrogen molecules was successfully determined by H-1 nuclear magnetic resonance (NMR), avoiding the intervention of neighboring molecules such as in hydrogen occluding materials (free hydrogen). The measurement was conducted with double walled NMR sample tube taking into consideration the change of hydrogen pressure. The inner tube was filled with standard substance (DHO in D2O at 4.8 ppm). The chemical shift of free hydrogen molecules was determined to be 7.40 +/- 0.01 ppm at 0.18 MPa, 25 degrees C, which is different from previously reported chemical shifts of hydrogen gas with intervention of neighboring molecules. (C) 2010 Elsevier B.V. All rights reserved.