Protest about taxes put on oil (13)
I believe the answer is:
expostulation
'protest' is the definition.
(thesaurus)
'about taxes put on oil' is the wordplay.
'about' indicates anagramming the letters.
'taxes'+'put'+'on'+'oil'='taxesputonoil'
'taxesputonoil' with letters rearranged gives 'EXPOSTULATION'.
(Other definitions for expostulation that I've seen before include "Protestation" , "Expression of strong disagreement" , "Remonstration" .)