2002 Dodge Caravan Fuel mileage

first is there a "check engine" light on, if so the o2 censor could be your problem

With the new ethanol mixed
gas mileage went down and fuel price going up and up

Not every check engine light caused by an o2 sensor
you need to have it checked for codes
or you can do the key cycle to retrieve the codes
check fuel filler cap
check for fuel leak
check wires
check o2 sensors
and the list goes on and on
codes will help pin point the troubled area and the cause
let me know