The most common and most likely answer to this crossword clue is the 9 letter word TALKATIVE
I've seen this crossword clue in Independent
T
A
L
K
A
T
I
V
E
More clues leading to the result TALKATIVE
- Take vital supply yielding plenty of gas
- Strained at, like vat full of gas?
- Like a TV broadcast in pursuit of acknowledgment? That’s saying a lot
- Take vital moves, providing a running commentary?
- Gassy valet with a kit for new treatment
- Effusive lecture on musical recalled
- Being chatty makes Kate vital
- Work’s ending at four — with story going round that’s gossipy
- Kit a valet misplaced being chatty
- Glib speech before Ms. Peron returns
Buddy explains!

The straight part
We know that "gassy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gassy = talkative.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 TALKATIVE mean?
TALKATIVE adjective- Tending to talk a lot.
- Speaking openly and honestly, neglecting privacy and consequences.