It is quite possible, under these 7 situations:

You are cheated by the gas station you use before

Road condition are different: wind, ascend, altitude.

speed you drive, patern of accelaration, load, tire tread. tire pressure, AC on/off, window down.

Recent repair, maintainace work improve effeciency.

Miscalculated before, my 88 accord had 37 mpg highway.

Odometer malfunction (or become accurate now).

Your memory does not serve well.