If this is the type of gas valv3e you are asking about.....
PB Blaster, Liquid Wrench etc .....liberally spray/soak it
Try to tighten slightly then unscrew it using a LARGE Channel Lock Pliers...grab body of gas valve with pliers
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31