Crude oil has a mix of many different hydrocarbons, the most valuable of which are the smaller, “lighter” molecules that are used to make gasoline and jet fuel.
Light crude has a greater percentage of these light components and less of the heavy components, which are used to make less valuable, tarry petroleum products. Sol this is what they mean when they say “light crude” or “heavy crude”.
“Sweet” and “Sour” means how much sulfur is in the crude oil. Less sulfur is better because it is much easier to refine, burns cleaner, and has a better odor. Sour oil has more than 0.5% sulfur.
Because there is so much crude oil in the world, everybody wants to buy the “light/sweet” crude, though there is far less of it available than “heavy/sour” crude. And refineries definitely prefer to refine light/sweet, as is is much cheaper, cleaner, and easier to refine.
The major producers of sour crude oil include:
North America: Alberta (Canada), United States’ portion of the Gulf of Mexico, and Mexico.
South America: Venezuela, Colombia, and Ecuador.
Middle East: Saudi Arabia, Iraq, Kuwait, Iran, Syria, and Egypt.
Not everyone. Many refineries in the US already spent billions of dollars to upgrade our refineries to efficiently process heavy and sour crude. It is cheaper and it has more BTU content. They would have to spend even more money now to switch back to light oil which is more expensive. Spending money to have higher cost is not what they want to do.