Waste oil comes from an array of different sources, including do-it-yourselfers, auto shops, manufacturing companies, electric generating stations, etc.
Some of this oil (including a portion of the oil skimmed from oceans following industry accidents) is simply burned off. Waste oil that's too contaminated to meet environment laws. How is oil recycled becomes a big environmental problem now.
And if it's been disposed of properly, waste oil can be collected and recycled, prolonging its usefulness.
General Public/Do-It-Yourselfer: You can take your oil to a certified collection center. Many communities have curbside recycling programs that allow you to leave your oil at the curb (properly packaged). Or you can have your oil changed by a service station that recycles the oil for you.
Businesses: Businesses that generate small quantities of used oil can use the same options that the general public uses.