Yea it's not good. Usually the 02 sensors but there are other things that can cause it too like an out of spec coolant temp sensor telling the computer that the coolant isn't hot enough so it dumps more fuel into the motor. Bad for MPG and bad for the cat. Leaky injectors can also cause that but that is much less likely than the 02's being bad.
When was the last time they were changed? Should be done every 50-60 thousand miles. I change mine earlier. Get Mopar or NTK. NTK makes the Mopar sensors. Change them both at once if that's your plan. Disco the battery when doing it.
Are you getting less than normal fuel economy? Unless you've noticed poor MPG's as of late, I would suggest cleaning up the tip a bit with some steel wool or a scotch brite pad first and see how long it takes for the tip to turn black again.
At this point your vehicle is 15 years old and it may just be normal carbon build up on the exhaust tip. Of course if you are unsure of the age of your O2 sensors, it couldn't hurt to replace them anyway. FWIW, Rock Auto had the best price on them when I replaced mine this past winter.
__________________ His: '00 WJ 4.7 Limited- Some stuff