Oil in USA revived a southern state (9)
I believe the answer is:
louisiana
'southern state' is the definition.
'louisiana' can be an answer for 'state' (Louisiana is an example). I am not certain of the 'southern' bit.
'oil in usa revived a' is the wordplay.
'revived' indicates anagramming the letters (I've seen this in other clues).
'oil'+'in'+'usa'='oilinusa'
'oilinusa' anagrammed gives 'louisian'.
'louisian'+'a'='LOUISIANA'
Can you help me to learn more?
(Other definitions for louisiana that I've seen before include "Southern United State on the Gulf of Mexico" , "IOU a snail over in the US state" , "US southern state" , "State named for French king" , "that's near Mississippi" .)