Drink in drunken bout, mostly restrained by oil company (8)
I believe the answer is:
espresso
'drink' is the definition.
(espresso is a kind of drink)
'drunken bout mostly restrained by oil company' is the wordplay.
'drunken bout' becomes 'spree' (I've seen this before).
'mostly' means to remove the last letter.
'restrained by' indicates putting letters inside.
'oil company' becomes 'esso' (Esso is an oil company).
'spree' with its final letter removed is 'spre'.
'spre' placed inside 'esso' is 'ESPRESSO'.
'in' acts as a link.
(Other definitions for espresso that I've seen before include "Seep Ross into the coffee" , "Italian-style coffee" , "Type of coffee" , "Kind of shot" , "This may keep someone awake!" .)