XP

Experience Points (XP) are a numerical quantity that dictates your level and your progress in that level. Your experience points are shown (in multiplayer) on the bottom of the screen with a yellow meter. When you gain experience points, it becomes green and resets when you achieve the next level.

The Experience Meter is only available in Call of Duty 4: Modern Warfare, Call of Duty: World at War, and Call of Duty: Modern Warfare 2. Experience points are also available in Call of Duty: United Offensive but there is no experience meter and the ranks reset when you end or exit a match.

Call of Duty: United Offensive
You only have to kill enemy players; destroy bases in the Base Assault gamemode or capture flags. You start as a private-first class and the top rank is Sergeant. The ranks allows you to carry more grenades, satchel charge and a pair of binoculars for artillery strike.

Call of Duty 4: Modern Warfare

 * Killing the enemy. You gain 10 points per kill in Team Deathmatch (all forms) and Sabotage. 5 points are earned for killing in Free for All, Headquarters and Domination. You can gain 50 points per kill in Search and Destroy, as no respawns are permitted; the life is worth more. Kills in Cage Matches are worth 20 points. If you kill when using Last Stand perk, double points will be earned. In Headquarters or Domination, you score an extra 5 experience points for kill an enemy who is within an objective capture range (i.e. within a Domination flag).


 * Assisting in the death of an enemy. If you injure an enemy but do not kill him and he dies before his health is fully regenerated you are awarded an assist, 2 experience points for matches which grant 10 exp a kill, 1 for kills which grant 5 exp a kill, and assists are impossible to achieve in Free-for-all mode.


 * Completing challenges. Challenges are a new method to gain experience points. Challenges have some requirements to be fulfilled before the reward is available. For example, for marksman challenges, you need to kill the enemy using the pertinent gun or in expert challenges, you need kill the enemy via headshots with the gun. There are also challenges that require you to do other, more varied tasks, for example, the "think fast" challenge requires you to kill an enemy by directly hitting the enemy with a Fragmentation Grenade.The challenges involving guns gives either attachments or camouflages as an addition to experience points. Other challenges give only experience points.


 * Additionally: The game gives you some bonus points for your performance when the match ends as a "Match Bonus".
 * As of the release of MW2 you permanently receive double XP on all kills, in all game modes.

Call of Duty: World at War
You can gain experience points in the same manner as you do so in Call of Duty 4: Modern Warfare, but also by:


 * Cooperative (Co-op) gameplay. This is a new mode where you play the missions in normal gameplay but with 2-4 players. You can do exclusive challenges when playing in Co-op. Remember that in Co-op ONLY the XP gained from Co-op challenges count for your level, the XP earned in the Co-op missions for kills or objectives do NOT count. Playing Nazi Zombies does not gives any experience points. Playing in split screen cooperative mode also does not give any experience points


 * Completing vehicle challenges
 * Killing a dog: this gives 3 points in all game modes except Free for All (2 points) and Search and Destroy (not confirmed)


 * Reviving a teammate whom is using Second Chance. This gives you 2 points.

For example in Team Deathmatch:
 * Gaining an assist. This is more complicated than Call of Duty 4: Modern Warfare as the amount of experience points gained is proportionate to the amount of damage inflicted towards the enemy. This is given in multiples of 5ths of the amount of XP given for a kill. The only exception is Search and Destroy, where all assists are worth 25 XP.

10 points for a kill.

2 assist points for at 1-39% of damage given.

4 assist points for at 40-59% of damage given.

6 assist points for at 60-79% of damage given.

8 assist points for at 80-99% of damage given, includes putting an enemy in Last Stand with a teammate "stealing" the kill.

Call of Duty: Modern Warfare 2
The experience system In Call of Duty: Modern Warfare 2 has been completely redone. Instead of just getting XP for kills, you get it for many different factors involving the kill such as:


 * Base Kill Award - 100 in Team Deathmatch and Sabotage, 500 in Search and Destroy, 200 in Personal Fight (third person) and 50 in other modes.


 * Payback! - Kill an enemy who has killed you previously. +50XP Getting this for a particular opponent will reset it until they kill you again.
 * Buzzkill! - Kill an enemy who is 1 kill short of acquiring a kill streak reward. +100XP
 * Bulls-eye! - Kill an enemy with a throwing knife. +50XP Becomes 0XP at later levels.
 * Flag Runner! - Picked up the flag in a Capture the Flag match. +50XP
 * Stuck! - Stick a Semtex grenade to an enemy. +50XP
 * Rescuer! - Save a wounded teammate +50XP Kill the person attacking him
 * Hijacker! - Steal an enemy care package. +50XP Sometimes +100XP, later becomes 0XP
 * First Blood! - Be the first person to get a kill in a match. +100XP
 * Offense! - Kill a defender. +50XP In an objective game, kill an enemy who is near a point/flag they control.
 * Defense! - Kill an attacker while near a point/flag you control in an objective game. +50XP (Does not matter if done by air support as long as you are near your own flag)
 * Comeback! - Recover from a streak of deaths. +50-100XP More dependent on amount of deaths in death-streak
 * Position Secure! - Take an objective. +150XP
 * Double Kill! - Kill two enemies in quick succession. +50XP
 * Triple Kill! - Kill three enemies in quick succession. +75XP
 * Multi Kill! - Kill four or more enemies in quick succession. +100XP
 * Longshot! - Kill an enemy from a distance. +50XP (Score a kill beyond the minimum damage range of a weapon that isn't a sniper rifle. Sniper rifles can also get longshots, shotguns cannot)
 * Share Package! - A team-mate saved your Care Package from the enemy! Multiples of 50XP depending on the number of kills usually required for the reward. (eg. a UAV will give +150 EXP, as it requires 3 kills to acquire normally)
 * One Shot One Kill - Kill an enemy who has full health with one sniper rifle shot. +50 XP
 * Flag Return - Return the flag. +50XP
 * Headshot - Kill an enemy with a bullet to the head. +50XP +500XP in Search and Destroy, despite saying +50
 * Crowd Control - Make an excellent distraction while a teammate kills the player shooting the shield. +50 for the assist, more for bullet damage absorbed by shield.
 * Afterlife - Kill an enemy while dead. +25XP
 * Assisted Suicide - Injure an enemy before he kills himself. +350XP
 * Execution! - Kill someone who is in Last Stand or Final Stand with a headshot. +100XP
 * Avenger - Kill an enemy immediately after they have killed a teammate. +50XP
 * Saboteur! - Plant the bomb. +1000 in S&D, +200 in Sabotage and +100 in Demolition.
 * Ninja Defuse - Defuse a bomb almost immediately after it has been planted (On S&D, Sabotage or Demolition). +1000XP
 * Hero! - Defuse the bomb. +1000 XP if in Search and Destroy, +100 if in Demolition, +150 if in Sabotage.
 * Heroic! - Get a capture point while in last stand. +200 XP
 * Assists give 200 XP in Search and Destroy and 1/5 of the base kill award on the rest of game modes.
 * Destroying a killstreak reward:+0 for Care Package Little Birds, +50 for UAVs and Counter-UAVs, +100 for turrets, +200 for Attack Helicopters, +300 for Harriers and Chopper Gunners, +400 for Pave Lows and AC130s.
 * Calling in a killstreak reward: +100 for 3-4 killstreaks, +150 for 5 killstreaks, +200 for 6-7 killstreaks, +250 for 8 killstreaks, +300 for 9 killstreaks, +350 for 11 killstreaks, +500 for EMP, +1000 for Tactical Nuke.