NY Mercantile Exchange. You will need to open an account with a seated broker. Typically they want you to deposit at least $5000. You can then buy call options or just a futures contract as far out as 2-3 years.
While it is true that you CAN buy futures contracts (or options on same), you had better be prepared to lose big suddenly. Casual dabbling in these markets can cost you big. I know. I’ve done it. I even made good money for a while. What happens is you become convinced of how smart you are with a little success. Usually as soon as you think you can time tops and bottoms in these markets, you blow up.
Cardinal rule: NEVER risk more than you can afford to lose. You won’t believe how quickly futures markets can turn on you until it happens, then it is too late. (I wonder whether someone is going to be desperate enough to start a war: Iran mining Gulf of Hormuz, etc. Historically, it doesn’t take all that much strife to cause crude prices to spike. Don’t expect to be able to cover your shorts if that happens. Your anticipated profits can be gone like so much wind....)