Some may try to rack up different definitions for the two but it can be hard to do because they mean the same thing. The main difference between fuel and petrol is where these terms are used. Petrol is known to be used in the UK. It is also used in India.
The United States of America, as well as its constituents, are more familiar with this item as gasoline. They usually call it gas for short. In the country where you are from, do you call the item petrol or gasoline? There is no wrong answer. What matters is that you already know that they are not different from each other.
There really is no difference between gasoline and petrol. Both words refer to the same thing which is the fuel that is used in an internal combustion engine. In the United States and Canada, people use the word gas as a shortened name for gasoline, which is used to fuel cars, lawnmowers and other things.
In the United Kingdom, India, Ireland, and probably other parts of the world, people use the word petrol. There are many examples of items called by two different words. For example, slices of raw potatoes that are deep fried are called French fries in the US but in the UK they are called chips.