Opinion piece includes tirade about oil (9)
I believe the answer is:
editorial
'opinion piece' is the definition.
(I've seen this in another clue)
'tirade about oil' is the wordplay.
'about' is an anagram indicator.
'tirade' with its letters mixed up with 'oil' makes 'EDITORIAL'.
'includes' acts as a link.
(Other definitions for editorial that I've seen before include "Paper's opinion piece" , "Article giving a newspaper's opinion" , "Newspaper article giving the editor's opinions" , "Article written" , "Article expressing the views of the publication" .)