Poor gas mileage E320

[PaulM]

I own a '98 E320 4matic wagon w/ 67K miles. I have owned the car for two years and put approx. 20K miles on it. In the last 3-4 months I have noticed that my gas mileage has gone down to approx. 16 mpg from a consistent 19-21 mpg previously. I am not getting any service lights indicating a service issue. I have replaced the air filter (which was dirty) but the poor gas mileage continues. Does anyone have any suggestions for things to check or replace to get the mileage back to where it should be.

Thanks for any feedback provided.

Sincerely, PaulM