The way to try to answer your question is to talk about some of the geological knowledge we have.
I'll turn to Monsieur Lavoie in a second to talk about how we know that reservoirs are under impermeable layers. The geology has acted to trap highly mobile materials over time. So that's part of the knowledge that we have, that there is a geological understanding of how long fluids and gases have been trapped in the subsurface, and they're trapped quite effectively. So geologically there's a—