Oil is called "black**" or "liquid**" for several reasons:
1.Economic value: Oil is one of the most important energy resources in the world and is essential for modern industry and transportation. It is the main fuel and is used in power generation, transportation, chemical industry, etc. Due to the huge importance of oil in the global economy, people give it a title comparable to **, highlighting its economic value.
2.Scarcity: Similar to **, oil resources are also limited. It takes millions of years for oil to form, and humans use it far faster than it can regenerate. Therefore, like **, oil is also seen as a scarce resource.
3.Volatility: Fluctuations in oil are often of great concern in international markets. This volatility can have a profound impact on the global economy. Because oil volatility is closely linked to economic and geopolitical events, it is often seen as an important economic indicator, which also helps to compare it to a "liquid".
4.Commercial Value: *has always been a type of business value and oil has a similar special status in industry and commerce. This commercial value makes people tend to compare oil to **.
Collectively, these designations emphasize the critical role, economic value and finitude of oil in modern society, as well as its special position in the international market. These characteristics are somewhat similar to people's perception of **, hence the praise given to oil.