Profitable source of energy promoted in America, oil perhaps (6)
I believe the answer is:
useful
'profitable' is the definition.
(associated in meaning)
'source of energy promoted in america oil perhaps' is the wordplay.
I cannot quite see how this works, but
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is present in the answer.
'america' could be 'us' (United States) and 'us' is found within the answer.
This explanation may well be incorrect...
(Other definitions for useful that I've seen before include "Handy, serviceable" , "Handy, practical" , "Effective" , "Utilitarian" , "Beneficial" .)