Gas supplying energy to most of Kent region (6)
I believe the answer is:
ethane
'gas' is the definition.
(I've seen this before)
'energy to most of kent region' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'to most of' means to remove the last letter.
'kent region' becomes 'thanet'.
'thanet' with its final letter removed is 'thane'.
'e'+'thane'='ETHANE'
'supplying' is the link.
(Other definitions for ethane that I've seen before include "Chemical" , "Athene (anag.); a colourless gas" , "Flammable gas; eat hen (anagram)" , "Fuel" , "Flammable hydrocarbon" .)