The most common and most likely answer to this crossword clue is the 6 letter word ETHANE
I've seen this crossword clue in The Times
E
T
H
A
N
E
More clues leading to the result ETHANE
- Gas in eastern district of Kent in short supply
- Egghead and chief of clan gas
- Online version of Macbeth is a gas
- Stupidly heat neon or other gas
- Beginning to erupt, chief of clan producing gas
- Restricted by Lambeth: a nerve gas
- End of joke by old king’s companion is a gas!
- Gas supplying energy to most of Kent region
- More than enough as storage for gas
- Removal of mass from firedamp produces gas
Buddy explains!

The straight part
We know that "Gas" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gas = ethane.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ETHANE mean?
ETHANE noun- An aliphatic hydrocarbon, C2H6, gaseous at normal temperatures and pressures, being a constituent of natural gas.
- The same compound, subjected to modification by replacing one or more of the hydrogen atoms with other radicals.