Low Gas Mileage

I have a 1997 Chevy Cavalier 2.2. I've measured my last 2 tanks of gas and I'm only getting 20 mpg. 1st tank was like 19 mpg with mostly highway driving at 75-85 mph. and the 2nd tank mostly city, to and from work and school. Anyone have any ideas what is wrong???

You're a leadfoot.

Thats what i figured but I was just checking if someone knows of something mechanically that could be causing this