EPA estimates for the 2000 E320 are 21/30 so getting just over 30 on all highway driving is not out of the question but is probably at the top end of what you'd expect. Lots of factors can influence mileage though. Wind speed and direction can have a huge influence. If you're driving into a 20 MPH wind at 75 MPH it's like driving 95 while if it is a tailwind it's like driving 55. Also, if it is hot and the A/C is running more your mileage will be lower than if it is cooler. Finally, like Len said, one tank is really meaningless. You can easily have ±1 gallon difference between fillups just on where the pump stops, even if you "top off" and that would have more than a 5% difference.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz