In the previous lecture we studied about the concept of capturing CO2 and store it underground. The underground is made up by various formation of porous rocks. To help safely store CO2 underground, we studied the concepts of porosity and permeability which are the two important characteristics of porous rocks which will determine the way CO2 move underground and thus, prevent it from leaking into the atmosphere. In this lecture we are going to talk about how to quantify the risk of potential CO2 storage sites and how mathematics can help us in this regard.