Oil's obtainable from the earth (4)
I believe the answer is:
soil
'earth' is the definition.
(earth can mean soil or dirt)
'oil's obtainable from' is the wordplay.
'oil's' anagrams to 'SOIL'.
Though, I am unsure how this is indicated.
'the' acts as a link.
Can you help me to learn more?
(Other definitions for soil that I've seen before include "Earth for growing" , "refuse" , "Top layer of the surface of the earth" , "In which plants grow" , "Earth; stain" .)