Gas for energy under cooking pot? (7)
I believe the answer is:
propane
'gas' is the definition.
(I know that propane is a type of gas)
'for energy under cooking pot?' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'energy' becomes 'e' (physics symbol as in E=mc2).
'under' is a charade indicator (letters next to each other) (below, in a down clue).
'cooking pot?' becomes 'pan'.
'e' put after 'pan' is 'pane'.
'pro'+'pane'='PROPANE'
(Other definitions for propane that I've seen before include "A hydrocarbon gas" , "Type of gas" , "Gas used as fuel" , "Bottle gas" , "gaseous fuel" .)