Measurements on 51 lithium-ion cells undergoing thermal runaway reactions within an autoclave setup are conducted in order to examine venting gas volume, composition and cell mass loss as well as to identify influencing factors on related parameters. A new method to calculate the volume of released gas during thermal runaway is proposed. Comprehensive examination of the gas analysis is done and compared to literature. Seven gas species (CO2, CO, H-2, C2H4, CH4, C2H6 and C3H6) are determined to be the most common within venting gas and an independence of gas composition from venting gas volume can be shown. Furthermore, energy density and cell capacity are found to be an influencing factor of venting gas volume, thermal runaway onset temperature and mass loss, thus severity. Finally a difference for pouch and hard case cell formats in solid to gaseous mass loss proportion is discovered and explained.