 In Lesson 3, we will take a quick walk through a refinery and go through some different kinds of processes. There are four types of processes in a petroleum refinery. They are separation processes which are essentially physical processes. No chemical change takes place in these processes, just physical separation. The second category is conversion processes where there is a lot of chemistry. We are breaking and making new chemical bonds so that we could produce the fuels in quantities that we want, in the yields that we want. The third kind of process is finishing process which is really to make sure that any product leaving the refinery is compliant with performance specifications as well as environmental regulations. The fourth kind of process is supporting process. These are essential processes to make sure that whole refinery functions and all these processes actually do perform their function in essence or their objectives. Now as we go through this refinery, we will see that there are certain areas of focus. Most recently, the refineries have focused on upgrading heavy oil. When we say heavy, we really refer to the high density crude oil. High density crude oil typically has a high aromatic hydrocarbon content and these crews are difficult to process, more expensive to process. So we will talk about some basic strategies how one could upgrade these heavy, highly aromatic crude oils into the desirable products which tend to be lighter, that means lower density such as gasoline, diesel and jet fuel.