i get ~350km er tank if i'm agressive in the city and 500+ if i cruise a lot on the highways.. there's definetly something wrong with your S

 

If you know you have a bad o2 sensor then thats probably the issue, the computer is probably having a hell of a time keeping an optimum AFR under closed loop operation and you're probably running rich as hell constantly. How do your exhaust tips look? You're probably also zapping your cat if its not dead already.

 

I also think that the o2 sensor is the problem.

 

I used to have a bad primary O2 in another Honda. It ran so rich that a cat would last less than a week on it. Went through 3 cats before I just gutted the thing

 

Also, is your air filter clean? I changed mine at 30k miles and it helped my MPG dramatically.

 

You've already pointed out some pretty obvious causes, get them fixed. A bad O2 sensor will definately contribute to bad mileage, and so will a clogged cat. While you at it, do some of the stuff mentioned above. Air Filter, Tire Pressure, etc.

If all that fails then, try getting opinions on the internet...

 

max i had ran a full tank on my ap2 about 305 miles, till i hit up the gas station.i was like woww,but normally it'll probalby get 280 and up.

 

Damn...you need to bring your car in for a full check up. I just hit 160 miles on half a tank....70% hwy/30% city.

 

i only hit 160 on my last fill up, but it was all city driving.. i am not sure if the s/c has much to do with it? my friends with sc'd S's have way better mileage than i do.. my average mileage per-tank is around 180 with mostly city driving. however, combined with highway, i think the max i hit was 250 miles on one tank.

 

Do you have a yellow box or other speedo / odo calibration device?

Your 160 miles might actually be 220 with the 18 inchers?