The number after US crude oil actually refers to the futures contract month of US crude oil, and US crude oil 1 actually refers to the futures contract of US crude oil 1, which will be delivered on 1 (the third Friday of the month is the note), and so on.

What we usually say about the price of American oil actually refers to the main contract. Generally, the main contract of US crude oil is the contract of the current month (if the contract of the current month is delivered on the third Friday of the current month, its main contract will become the contract of next month).