Crude oil is a collection of mostly hydrocarbon molecules with different amounts of other molecules. The amount of different hydrocarbons varies also. (Hydrocarbons are chains or rings of carbon molecules with hydrogen attached all around. Different petroleum products are just different sized hydrocarbon molecules). Some pockets of crude oils are mostly long chain molecules, heavier oils asphalt etc. Other pockets have mostly very short chain molecules, methane, propane etc. natural gasses. Sweet crude oil contains a mixture of different length hydrocarbons and minimal abouts of other molecules (mostly sulfur based molecules. So sour crude contains more sulfur based molecules then sweet crude.) Now comes the fun part. Refining is basically distilling and seperating out all the different lengthed hydrocarbon molecules into products with all the same length molecules. So your question is how many gasoline length molecules are in a barrel of crude oil? Well it depends. First the different grades of crude with have different amounts. Some grades lots of longer then gasoline molecules others have a lot of gasoline length molecules. So different crude oils will yield different amounts of gasoline length molecules. The sweet/sour grade is how much worthless, "you have to pay to put in the air" sulfur molecules are in the oil. So a sweet high grade crude has lots of gasoline molecules and very few garbage sulfur. Low grade sour has lots of sulfur and less gasoline length molecules. But we are not quite done yet because there is a proccess used at the refineries called "cracking". (my background is in science and chemistry hence the knowledge, but not in the oil buisiness so if you want to learn more about grading you will have to find someone with that background). Back to cracking. The refineries will test the crude, find the percentages of the different length hydrocarbons and then make decsions on how to refine that crude oil. We can add chemical compounds to the crude oil that will break the hydrocarbon chains. Knowing the percentages of different hydrocarbom molecules (different lengths) and knowing how different additives (with tweeks in rate and temp.) will break/ "crack" the hydrocarbons refiners can manipulate the amounts of different product they get from a barrel of that particular crude oil. Refering back to the earlier post, the more the refiner needs to test and crack the more it costs to refine the crude, but if the product is selling high enough that cost can be worth it, if not then no. So finally, refiners watch the markets. Towards the end of summer the refiners do less cracking and so produce more longer chained hydrocarbons that are fuel oils used for heating homes for the winter. Towards spring they will crack more to produce more shorter gasoline molecules. So the same grade of crude can produce different amounts of fuel oil or gasoline depending on how it is refined. How it is refined is based on demand and markets. Now refiners can not "crack" to produce only one product, they can only change the percentage of product. What percentage of gasoline they produce is dependent on the crude they start with, the market demands and the ability of their chemists manipulate the lengths of the hydrocarbon chains in that particular crude oil.
Other things that we get from crude oil is butane, methane, propane (many of these are burned off by the gasoline refineries but some is trapped, pressurized and sold. newer refineries are better at this then older ones), gasoline, fuel oils, deisel, kerosene, different grades of lubricating oils, asphalt and (here it comes) the starting product for making plastic. (This is sold to other companies that employ more chemists to manipulate those molecules into "mers" (long chains of carbon) and later polymers (many mers stuck together). So anything in your life that is made from plastic also comes from the refining of crude oil.
Right now the price of crude is artificially high. The refineries are booming!!! They can not refine all the oil that is now in storage. We are pumping and buying more oil then we can refine. World oil storage capability is almost full. Investors are buying and storing oil on the prediction that oil prices will rise. So right now they are paying more for oil not because of low supply but because of future expectations of even higher prices. Some of the biggest buyers of oil right now are investment firms. Gasoline prices are high because the refineries are maxed out but consumers want more so they can sell at high prices. (Don't like it? try to find another refinery that has some extra gasoline to sell. There aren't any right now) finally, why not build more refineries? Well for that you have to ask Exxon and the other large oil companies. They are not building new refineries and why should they. Exxon continues to break the worldwide quarterly profit record over the last 18 months. (exceeding $10 billion PROFIT!! every 3 months). Also refineries cost big bucks to build and are a royal pain in the *** because of all the environmental regulations. But that is a whole other thread. I hope this answers some questions about how much of what and why we get from a barrel of crude oil.
