Crude trader I left in sultanate (6)
I believe the answer is:
oilman
'crude trader' is the definition.
(someone trading in crude oil)
'i left in sultanate' is the wordplay.
'left' becomes 'L' (common abbreviation).
'in' is an insertion indicator.
'sultanate' becomes 'oman' (I've seen this before).
'i'+'l'='il'
'il' put into 'oman' is 'OILMAN'.
(Other definitions for oilman that I've seen before include "Person involved with crude" , "Owner of company that sinks wells for fuel" , "One working in the "black gold" industry" , "Worker" .)