Company dealing with oil from wreck (5)
I believe the answer is:
total
'wreck' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for total that I've seen before include "given by 8 [ADDING MACHINES]" , "outright" , "Ruin" , "Sum, aggregation" , "Damage beyond repair" .)