Natural resource maybe helping to make millions (3)
I believe the answer is:
oil
'natural resource' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for oil that I've seen before include "Greasy liquid" , "valuable commodity" , "what can be seen on iceberg" , "Liquid fuel" , "Slippery liquid" .)