Arbitrage, that is, spread trading. There is an unreasonable price difference between the two varieties, but the price difference will return to a reasonable level after a period of time, during which the price difference can be used for trading. This classification is based on different reasons for price differences.

Internal arbitrage and price difference changes are caused by internal factors such as coup and special circumstances.

Correlation arbitrage and price difference changes are caused by the internal correlation between varieties, such as the substitution of soybean oil and palm oil, and the upstream and downstream relationship between coking coal and coke.