The study, based on some cases distributed along the Northern Apennine chain, led to identify an extreme variety of the natural settings, where fluids leak out from reservoirs of different ages, which are deformed at different times and as a consequence of different stress regimes (compressional or late-orogenic extensional). A common point is the presence of good reservoirs of variable volumes, in several cases disrupted by recent deformation. These reservoirs drain hydrocarbons that leak from deeper reservoirs or that are formed by a source that is deeply buried in the chain, but still producing. Minor biogenic gas accumulations characterize the eastern mountain front, that was more recently deformed.