My fuel gage would drop at twice the rate of consumption. After a restart, the fuel level would display correctly, but as I drove it would start to drop twice as fast again. The computer information in the dash display was always correct though as far as consumption was concerned, but the range was way off. It required a new right side sending unit to correct it.

2002 X5 3.0 259,650 miles
2004 325i 115,000 miles