Me and a friend went to chicago, I was a medic he was spec ops. He blew up a car and set himself on fire, I healed him got myself around 150xp. I had an idea, because spec ops can give medics the healing orb things, He should stay on the car, throwing me ammo, and me continuasly healing him.
It worked! Although with 1 medic and 1 spec ops, the medic runs out of the healing orbs after about 7000xp worth of healing.
To improove this, I decided to ask my other friend to join in. So we had 1 medic (me) and 2 spec ops.
This meant 300-400xp every health orb i shot, and it was sustainable!
We did this for about 5 mins and eventually I got up to 99999xp, to my surprisment, i found the MAX xp you can get in a single co-op game is 99999xp, i will not go any higher!
So we all had a go, 3 players with 99999xp!!! that was very funny!


So to do this xp glitch/hack thingy you need:

1 Medic (This is the guy that will get the 99999xp)
2 Friends as spec-ops (these will get around 14000 xp if he gives ammo to the other two (if you take it in turns))
A chicago co-op map, just luck, need one with a car, find one, blow it up so its on fire. Note: cars only stay burning for about 6 mins, just enough time for 1 player to get 99999xp.


1. Fill the medic up with health orbs (10 without the upgrade)
2. Find the car, blow it up so its on fire...
3. Both Spec-ops people jump on the car, medic holds r2 just before(makes up for any lag)
4. Spec-ops continue throwing their ammo ( with 1 spec-ops guy, the medic will eventually run out, with 2 spec ops, the medic doesnt run out...and the medic get 2x more xp)
5. Just continue for around 5-6 mins, there you go 99999xp for your medic!
6. Do the same for the other players.

Other things:

You could have more than 2 spec ops, the medics xp will go up insainly fast if you have more players:
150xp per spec-ops on fire:
300xp for 2 spec-ops,
600xp for 4 spec-ops, ETC
This is around every 3 seconds!

Have fun!