Flow easily with crude oil making capital (7)
I believe the answer is:
tripoli
'capital' is the definition.
(capital of Libya)
'flow easily with crude oil' is the wordplay.
'flow easily' becomes 'trip' (as in tripping off the tongue).
'with' means one lot of letters go next to another.
'crude' is an anagram indicator.
'oil' with letters rearranged gives 'oli'.
'trip'+'oli'='TRIPOLI'
'making' acts as a link.
(Other definitions for tripoli that I've seen before include "powdery deposit" , "Libya's capital" , "Lebanese port" , "Libyan city" , "Middle East port" .)