Queen, involved in lousy oil transaction, makes a speech (9)
I believe the answer is:
soliloquy
'a speech' is the definition.
(soliloquy is a kind of speech)
'queen involved in lousy oil transaction' is the wordplay.
'queen' becomes 'q' (chess abbreviation).
'involved in' is an insertion indicator.
'transaction' indicates an anagram (letters moved around as in a transaction).
'lousy'+'oil'='lousyoil'
'lousyoil' with letters rearranged gives 'solilouy'.
'q' inserted within 'solilouy' is 'SOLILOQUY'.
'makes' acts as a link.
(Other definitions for soliloquy that I've seen before include "Dramatic speech presenting "unspoken" reflections" , "Speech performed to oneself" , "Monologue" .)