Checked the codes

According to my dad, this isn't the first time my car has had oxygen sensor problems.

relatively sure it only has one o2 sensor, As for the negative effects a bad has, mainly extremely poor gas mileage

No wonder why my gas mileage hasn't been as good lately. It's still been better than a lot of vehicles, but not as good as it used to. It sat most of the summer, but driven around the block once a week. Went on a 24-mile round trip once and used up 7 gallons of gas total from the trip and the going around the block. I think if I recalled correctly, when I averaged it out, I only got around 11mpg. I have, however, started going back to school and it's 5 miles (round-trip) a day. Gone 16 days so far. (80 miles) A little bit more driving done that would probably be another 10 miles or so. Gas level is around 7/8 on the guage, but it's probably more like 5 or 6 gallons of gas used. That would be around 15 mpg to 18, which is still lower than it is supposed to be. I believe in the city it's supposed to be around 24mpg and highway 30 or 31. I remember I could used to go to my grandma's house (110 miles round trip) and still be on full when I got back home. (probably used 3 or 4 gallons of gas) It'd be interesting to see what it would do now.