Notice that the river is always changing. You will encounter islands, narrow channels, bays, and lots of enemy ships and aircraft moving to block your path. Also, the farther down the river you fly, the fewer fuel depots you'll find. In some areas, fuel is quite scarce, so you'll really have to move if you want to survive. Always keep an eye on your fuel gauge.
Fuel is used up at a constant rate, regardless of speed.
The slower you fly over a depot, the more fuel you receive. A bell will sound while you are refueling. The sound changes to a higher pitch when your fuel tank is full. Losing a Jet. If you have a reserve jet left, you restart play at the same section of the river where you crashed.