Sudden, dramatic decrease in MPG

[CorvallisBMW]

Over the last 2 weeks my mileage has plummeted. It went from about 25mpg on a round trip to work, down to around 21 mpg. And over the previous week (to work 5 times and back, plus a few errands) my average for the tank dropped from my normal of about 24mpg down to 18! I used to get around 250 miles before dipping to around 1/8 of a tank, now I'm only getting around 180-190. What could cause such a sudden drop like that? I've been through 3 tanks of gas in the last 2 weeks and they've all been super low mpg like this. What gives? The car is running perfect, no funny noises/smoke/fuel smell/leaks/etc

[bmw325csi]

clogged fuel filter?

edit: Why dont you seafoam it?

[CorvallisBMW]

clogged fuel filter?

edit: Why dont you seafoam it?

done and done already

[kronus]

Check if any of your brakes are dragging. Aside from that, see if the engine is throwing any codes.

[CorvallisBMW]

checked, No brakes are dragging including the ebrake. Could a clogged fuel filter really do this? I replaced it less than 5000 miles ago

[DCColegrove]

Check the O2 sensor.

Also: Did you change the fuel you are using?