Here's why:
* Petrol is a substance, not a group of living things. Collective nouns are typically used for groups of animals, people, or things with similar characteristics.
* It's not something that naturally forms groups. You might have a "pool" of petrol, but that's more of a descriptive term than a collective noun.
Instead of a collective noun, you could use more general descriptive terms like:
* A supply of petrol
* A quantity of petrol
* A tank of petrol
* A barrel of petrol
* A pool of petrol
Let me know if you have any other word-related questions!