[SOUND] What is oil? Oil is probably the most important fossil fuel commodity. A little over a third, about 35% of the US energy supply is from oil. If we look worldwide, a third of all of the energy that's used in the world, comes from oil. The single highest category. So, what is it? Well oil is a fossil fuel. Oil is created by dead plants and animals, yes we're talking dinosaurs and big, giant ferns, but off course the predominant volume of these dead plants and animals is not the dinosaurs or the giant trees, it's probably the microscopic organisms, the plankton, the small plants. These died, they fell to the bottom of a marine environment, saltwater, and that's critical. These are things that died and ended up falling to the bottom in a saltwater environment, marine environment, get covered over, over time, get buried under higher pressure, higher temperature, and then you throw in time, on the order of 100 million years, and you got oil. We'll talk about geology because the oil has to be trapped for that long. It can't just leak out. It is a liquid. But if it was trapped, and it was under those high temperatures and pressures, hydrocarbon matter, living matter, turned into oil. So, in some ways, you could call it, quote, renewable because certainly things are dying today and getting buried in the sea. Except it'll take millions of years or tens of millions of years to turn it back into something like oil. So, the rate at which we are producing, quote, new oil is at such an infinitesimal rate to the rate that we're using it, it's not a reliable resource. It's a resource that a planet is fairly rich in. After the stuff is buried, it turns into carbon chains, predominantly single carbon chains. And the most prevalent constituent of crude oil is a carbon chain that has eight carbons. C-C-C-C, that's four, C-C-C-C, eight carbons, all in a row, with hydrogens on them. This is the molecule octane and of course you know it by a much more common name, gasoline. Why does gasoline have octane ratings? Because it's predominately octane. So, is crude oil only gasoline? Well, clearly not. Here you can see a jar of crude oil. Crude oil is about 25% gasoline. And you wouldn't know that. Because most people the only time you'll ever see crude oil is when it's on seabirds in an oil spill, right? Oil tanker spills! Go out to the site, you see this thick gloppy stuff washing up on the beach and coating the birds. Well yeah, that's part of crude oil because all the lighter stuff, all the things like gasoline evaporated away, leaving the heavier hydrocarbons in place that did not evaporate and are causing such a mess. Crude oil itself is this fairly thin stuff, since it's got a lot of lighter hydrocarbons in it. It's not only the eight chains. Everything from about five carbons, to maybe 12, 13 carbons, is a liquid. And if that's a liquid, we call it crude oil, it's oil, petroleum. So you might be wondering, what happens if all these dead plants and animals accumulate not in the salt water, but in a freshwater bog. That makes coal, which is a very different beast. We'll have a whole topic on coal and we'll tell you more about it and show it to you. You also might wonder, what happens to the lighter carbons, the ones with fewer than five? Well, they're not a liquid, they're a gas, and that's what natural gas is. Natural gas is mostly methane, CH4. You have ethane, C2H3, propane, C3H8, butane C4. So, the lightest hydrocarbons are formed the same way that oil is formed, but since it's in the gaseous state instead of the liquid state, we call it natural gas. How about on the other end? What about the things that aren't liquid but are still of the same type of hydrogen carbon compounds that are higher in number, 13, 14, 15 higher? Well, those substances aren't liquid at normal temperatures. They're something more like tar. Shouldn't there be deposits of those as well? Well, yes there are. In fact, since they weren't a liquid, those deposit don't even need [COUGH] some kind of geological trap. That is what we call tar sands, or heavy oils. Hydrocarbons form the same way, but for longer chains. And they need to be dug up, and if you warm them up, they turn into a liquid. [MUSIC]