Stumble on crude oil in Mediterranean port
I believe the answer is:
tripoli
'mediterranean port' is the definition.
(I've seen this in another clue)
'stumble on crude oil' is the wordplay.
'stumble' becomes 'trip' (synonyms).
'on' is an insertion indicator.
'crude' is an anagram indicator.
'oil' anagrammed gives 'oli'.
'trip' inserted inside 'oli' is 'TRIPOLI'.
'in' is the link.
(Other definitions for tripoli that I've seen before include "North African capital" , "where there's been regime change" , "Polish" , "Libyan city" , "Place in Libya" .)