I need to replace the O2 sensor on my 99 Oldsmobile; where is it and can I do it? 1999 Oldsmobile Intrigue GL

It depends on which o2 sensor is bad. you have 2 on your car ones an upstream o2 sensor which is before catalyic convertor the other is a downstreem o2 which is located after the cat. they both range anywhere from 50.00 to 100.00 a peice. and there is a special tool to buy to change it. this is what it looks like. if you don't mind jacking your car up and placing jack stands under the car to support it. you should be able to replace it. besure to spray it real good with some penatrating oil like wd40 and let it soak for a while before trying to remove it.