African capital’s crude oil used on excursion (7)
I believe the answer is:
tripoli
'african capital's' is the definition.
(capital of Libya)
'crude oil used on excursion' is the wordplay.
'crude' indicates anagramming the letters.
'used on' means one lot of letters go next to another.
'excursion' becomes 'trip' (I've seen this before).
'oil' with letters rearranged gives 'oli'.
'oli' put after 'trip' is 'TRIPOLI'.
(Other definitions for tripoli that I've seen before include "where there's been regime change" , "Polish" , "Port city of Lebanon" , "City in Libya - city in Lebanon" , "Libyan city" .)