reserve petrol tank BrE
reserve gas tank AmE

Inside were a small reserve petrol tank, a red warning triangle, and a half-set of golf clubs.

Howard thought the pilot had jettisoned his reserve petrol tank, but he sent a reconnaissance patrol to find out what it was.

The shells still had enough energy to bash through the reserve petrol tank just beyond the panel and rip open the glycol header tank in front of that.

"But you also had a reserve gas tank."

The reserve gas tank is a fifteengallon plastic jug.