Possible Clues:

• Gas number
• Employed in the production of petroleum once at Shell
• Petrol has this running at once
• & 21 Across Rating in engine room marrying Commander Brown and Nurse Brown?
• High-__ (dynamic)
• Gas pump stat
• High-___ (powerful)
• C8H18
• Filling station number
• An isometric saturated hydrocarbon found in motor fuel