Green’s Dictionary of Slang

gas v.1

[gas n.1 (1)]

1. [mid-19C+] (also gas off) to chatter, to talk inconsequentially and continually, to offer only ‘hot air’.

2. [mid–late 19C; 2000s] (US campus) to deceive.

3. [late 19C–1910s] to boast.

4. [1940s] (US black) to tell, to inform.

In phrases

gas it (v.)

[1960s] (US campus) to do badly on an examination.

gas off (v.)

see sense 1 above.

gas round (v.)

[late 19C–1910s] to ferret out information in a clandestine manner.

gas someone up (v.)

[2010s] to flatter, to deceive.