 In lesson two, we will talk about the properties and classifications of crude oil. Because of the extreme complexity of crude oil, it is impossible to get the molecular analysis or the molecular composition. Because of this reason, people, even in the very early days of refinery, they developed some techniques to use easily measurable physical properties such as density or viscosity to make inferences about the molecular composition of crude oils. This information is very important for refiners to adjust operating conditions in many units that are all integrated in the refinery. So, to get these properties is really critical and they can be easily measured in the laboratory. Now, what is important and fascinating to see that some classification parameters or characterization factors were used using these easily measurable properties to make inferences on the chemical constitution, from chemical composition of crude oil, from physical properties to chemical composition. You know that crude oil contains essentially hydrocarbons that are paraffinic or naphthenic and aromatic. So, using these characterization factors, we could classify the crude oils into these three subcategories. But beyond that, if you do have information on the hydrocarbon composition, you could use a more sophisticated classification system to divide crude oils into six classes. Again, these are very important in terms of informing the refiners what to expect from the crude oil, how they can adjust the operating parameters so that they can produce the products that they would like and the properties of these products, the quality of the products to make these adjustments to reach these refinery goals and objectives in general. So, see you in class after this.