Wide--angle reflection seismic experiments were performed at the Storegga slide offshore Norway in 2002 with the goal to quantify the amount of gas hydrate and free gas in the sediment. Twenty-two stations with Ocean Bottom Hydrophones (OBH) and Seismometers (OBS) were deployed for a 2D and a 3D experiment. Kirchhoff depth migration is used to transform the seismic wide--angle data into images of the sediment layers and to obtain P wave velocity--depth functions. The gas hydrate and free gas saturations are estimated from the elastic properties of the sediment on the basis of the Frenkel--Gassmann equations. There is 5--15% gas hydrate in the pore space of the sediment in the gas hydrate stability zone (GHSZ). The free gas saturation takes the value of 0.8% for a homogeneous distribution of gas in the pore water and 7% for the model of a patchy gas distribution.