Why does your Hyundai Santa Fe 2001 run out of gas so quickly?

My Hyundai Santa Fe (2001) runs out of gas so quickly because two of my Oxygen sensors are bad and need to be replaced. They are causing my engine to run rich at this point and therefore reducing my gas mileage. I also have a broken fuel gauge that makes it appear that I have gotten only 200 miles to a tank. When really this isn't so. The cause of my fuel gauge being broken is the floater in the gas tank. This "floater" determines your fuel level and therefore moves the gauge. I actually get about 300 miles on my 17 gallon fuel tank but my gas gauge is on "E" after about 150 miles. I reset my tripometer every time I fill up so that I can keep track of my gas mileage. (Hope this helps.)