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 avabile in Call of Duty 4: Modern Warfare and Call of Duty: World at War. 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 binocular 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. If you kill when using Last Stand perk, double points will be earned.


 * Assisting in the death of an enemy. If you attack an enemy but do not kill him and he dies a short while after the attack 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".

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. Playing Nacht der Untoten does not gives any experience points. Playing in split screen cooperative mode also does not give any experience points


 * Completing vehicle challenges


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


 * 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.

Call of Duty: Modern Warfare 2
In this game, the XP system was completely redone. There are many XP bonuses for doing special things, including:
 * Payback! - You've taken revenge. +200XP


 * Buzzkill! - Stopped enemy short of a kill streak. +100XP


 * Bulls-eye! - Kill an enemy with a throwing knife.


 * Flag Runner! - Picked up the flag in a Capture the Flag match.


 * Stuck! - Stick Semtex on an enemy.


 * Rescuer! - Save a wounded teammate (kill the person attacking him)+50XP


 * Hijacker! - Steal enemy care package


 * First Blood! - You got the first blood. +150XP


 * Offense! - You killed a defender. +50XP


 * Comeback! - You've recovered from a streak of deaths. +100XP


 * Position Secure! - You've taken an objective. +150XP


 * Double Kill! - Kill two enemies at once.


 * Multi Kill! - Kill multiple enemies at once.


 * Triple Kill! - Kill three enemies at once.


 * Longshot! - Nice kill from a distance. +50XP


 * Share Package! - A team-mate saved your Care Package from the enemy! +550XP


 * One Shot Kill - One shot...One kill


 * Flag Return - You return the flag to it's "base".