Maybe oil one found in desert by harbour (8)
I believe the answer is:
portrait
'maybe oil' is the definition.
(a portrait might be an oil painting)
'one found in desert by harbour' is the wordplay.
'one' becomes 'I' (Roman numeral).
'found in' is an insertion indicator.
'desert' becomes 'rat' (ratting is a kind of deserting).
'by' says to put letters next to each other.
'harbour' becomes 'port' (I've seen this before).
'i' placed within 'rat' is 'rait'.
'rait' after 'port' is 'PORTRAIT'.
(Other definitions for portrait that I've seen before include "Painted likeness of a person" , "characteristic depiction" , "Person's picture" , "Artistic representation (of a person)" , "(Person's) painting" .)