Rich oil producer wasn't perfectly upright (4-6)
I believe the answer is:
well-heeled
'rich' is the definition.
(I know that rich can be written as well-heeled)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for well-heeled that I've seen before include "Affluent" , "Wealthy" , "Prosperous, rich" , "Comfortably off" .)