In this paper, a computational approach to the atmospheric dispersion that is associated with cryogenic releases of the gaseous fuels hydrogen and natural gas was attempted. A computational fluid dynamics (CFD) method was followed, using the code CFX 5.7 for the simulation of large-scale liquefied hydrogen and liquefied natural gas spill trials, which provided successful prediction of the concentration histories, against experimental records. The main outcome that was determined through the results was that fuel gases, such as natural gas and hydrogen, disperse as heavy gases rather than light gases during a cryogenic release, despite their positive buoyancy under normal conditions. This conclusion is of major importance from the standpoint of safety, in regard to chemical installations that handle liquefied gases, given that the gravity-driven dispersion of flammable gases increases the risk of ignition and, hence, accidental fire or explosion. Thus, the behavior of the released gas should be known when selecting the appropriate dispersion model that will be used in industrial safety studies. Furthermore, it was concluded that CFD may be effectively used in risk analysis procedures, providing reliable results even for the complex case of nonisothermal atmospheric gas release.