President stops oil company producing black fluid (8)
I believe the answer is:
espresso
'fluid' is the definition.
(espresso is a kind of fluid)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for espresso that I've seen before include "Drinks machine" , "Kind of shot" , "Coffee made under steam pressure" , "Type of coffee" , "strong drink" .)