What i want to do is make a oil leak catch fire and them lead it to the oil barrel whenever anything is thrown at it...How do I do that??

What about a string of colliders that overlap slightly? It isn’t super-efficient, but without any more details about your requirements it’s at least a very general solution. You can add more nodes to the string to simulate the oil leak growing, remove them if the leak gets cleaned up, and move them around if necessary.

You could have a fire particle effect and two colliders on each node: one for oil, one for fire, on different layers. Initially, the particle effect and fire colliders would be disabled. If a fire collider (e.g., thrown match, or a burning oil node) touches the oil collider, disable the oil collider and enable the fire collider and particle effect. Then this fire collider will trigger any oil nodes that it overlaps, and so on. You’ll have to use OnColliderStay() because overlapping oil nodes won’t trigger OnColliderEnter(), since they’re already overlapping. Alternatively, you could have just one collider and change the layer from oil to fire.

To enhance the effect, you could determine the direction from which the node caught fire (i.e., look at the vector between the collider and the node), and rotate the particle effect so it starts on the side nearest the collider and extends in the opposite direction.

For more specific use cases, however, you could avoid physics and devise something more efficient, such as a 2D texture/billboard, or a carefully-designed particle effect. The particle effect would probably give you the smoothest burn line.