Buying down can actually be understood as borrowing a barrel of oil from the market to sell it (for example, selling it at $50), and then hoping that the market price will fall, and then buying back the barrel at $40 and returning to the market (the actual number of oil barrels in the market remains unchanged). Then I earned a price difference of 50-40 = 10.

The so-called future is the difference between expectation and present. For example, if you order a cake, if the price of the cake appreciates tomorrow, you can eat it yourself or resell it to earn the difference. On the contrary, if you sell cakes, you naturally hope that the price of cakes will drop tomorrow, because cake subscribers still have to fulfill today's high-priced purchases (paid today).

Therefore, crude oil futures are just a change when everyone guesses that the supply is uneven. Supply exceeds demand, buy it, because there will be cheaper cakes tomorrow, and you should be selling cakes today; Demand exceeds supply, so it should be the cake buyer today, because it will be more expensive tomorrow.

Similarly, in fact, the same is true of investing in stocks. The basic logic is to sell high and buy low, but long is to buy low and then sell high, and short is to sell high and then buy low (the price of products will always fluctuate around the value, so there will always be fluctuations, that is, buying and selling will happen at the same time, but sometimes the buyer will make profits to the seller, and sometimes the seller will make profits to the buyer, depending on the relationship between supply and demand). It's just that the time is different, but investors should try to have a positive and negative direction, that is, which side of supply and demand this stock belongs to.