what kind of oxygen sensor do I use for my 2000 infiniti G20?

There are multiple part numbers for your Infiniti. Your O2 sensor performs different volumetric measurements during you drive cycle. Best advice, take a look at them from under the vehicle. Note the number of wires and their color. Then just unscrew the old and install the new. Not sure why you are changing them, they shouldn't even be a maintenance concern after seven years. Good Luck.

your car uses heated and nonheated o2 sensors, two befor the cat. convertes and two after the cat. They tell your onboard computer what the air/fuel mixture is befor and after the cat so it can regulate the fuel injectors and makc adjustments from there. When you buy your o2 sensors, the amount of wires will tell you front or rear and the plug that you plug into the factory harness will determine left or right. It isn't as tough as it seems,If you had a 4 cyl,you would only have 2, keep this in mind, front or rear-left or right hope that this helps

your best bet is to remove one o2 sensor at a time( with wires) mark its location and bring them all with you to your autoparts store and sort out the ones you dont need

i would also suggest that all o2 sensors be changed at once as not to give the cars computer bad info