out of gas
out of gas  {adv. phr.}
1. Out of fuel (said of automobiles). 
Be sure you don't run out of gas when you go on a long distance trip by car.
2. Rundown; depleted of energy; in poor physical condition. 
Mary said she had to take a break from her job as she was running totally out of gas.
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Source: A Dictionary of American Idioms

