run out of steam informal
run out of gas AmE informal

Others ask whether it might not just be that he has run out of gas.

Some had just run out of gas with no hope for getting more.

They would come to when the car had run out of gas.

By the time the car ran out of gas, he was dead.

Or so he'd thought until he ran out of gas.

No one wanted to run out of gas on the road.

"Do we keep going until you run out of gas?"

You asked: When will we run out of oil/natural gas?

The world is not yet running out of oil or gas any time soon.

About all I know for certain is that we're running out of gas.