I run Oblivion on max on 1600x1200 with HDR and 16x AF and no AA (don't really need it on 1600x1200) and depending on the city I usually get around 28-35 fps in the demanding areas. Some cities, when I look down a long road with lots of buildings, I get as low as 18 fps. I turned the resolution down and got the same exact fps so I not quit sure what to think. However that doesn't mean the whole game runs slow, most of the time I'm maxed out at 60fps and usually stay above 40fps most of the time. Certain parts of cities are the most demanding.
Although I also have my ini file tweaked to load more cells, and some memory based tweaks, so if your running on the default ini you may be getting different performance.