Due to Helium gas high solubility in hydrocarbons (see tab Scientific Principles/Solubility), Helium flow that comes from oil & gas deposits is considerably greater than in normal circumstances. This principle enables the correlation between Heilium and hydrocarbon presence.

 

The video below is quick demonstration of how the AGI's system works, there you can see the increase of Helium concentration in the detector while being in contact with a bottle containing petroleum.