Just a single song, or possibly duets about oil refining (8)
I believe the answer is:
solitude
'just a single song' is the definition.
I can't judge whether this definition defines the answer.
'possibly duets about oil refining' is the wordplay.
'possibly' is an anagram indicator.
'about' means one lot of letters goes inside another.
'oil refining' becomes 'oli' (I can't explain this - if you can you should believe this answer much more).
'duets' is an anagram of 'stude'.
'stude' going around 'oli' is 'SOLITUDE'.
'or' is the link.
Can you help me to learn more?
(Other definitions for solitude that I've seen before include "Avoiding company" , "Absence of company" , "Privacy" , "Lone state" , "Seclusion" .)