Good morning Luke. The fuel tank on the is200 is 70litres. I've driven the car pretty much to empty, the fuel needle resting on the stopper and I've only been able to squeeze 68litres in, so there are a couple of fail safes to make you think you need to stop and fill up, which is good.
If you click on my MPG banner in my signature, it will take you to my Fuelly page and you can see how often I've been able to pass 400 miles from a single tank. Admittedly, I do drive sensibly a lot.
My average over 14,000 miles is 31.5MPG and my last three petrol stops have shown my MPG as 32.4MPG, 32.6MPG and 32.7MPG. I'm due to fill up around Wednesday and I'm hoping my MPG to be higher again. I've done 410 miles so far on this tank and I'm still two notches away from the fuel light coming on.
Oh, and with my style of driving, I know I can get 50 miles from the car after the fuel light comes on. So if you do end up driving like me, the fuel light does not mean stop immediately. Lol.