Complete the following challenges to earn the corresponding amounts of XP:

CHALLENGE - HOW TO COMPLETE/(XP)
Headhunter - Kill 50 human enemies (1,000 XP).
Not Really a People Person - Kill 250 human enemies (2,000 XP).
Misanthrope - Kill 1,000 human enemies (5,000 XP).
War Criminal - Kill 2,500 human enemies (20,000 XP).
Lucky Shot - Kill 100 enemies with critical hits (1,000 XP).
Crack Shot - Kill 250 enemies with critical hits (2,000 XP).
Don't You Ever Miss? - Kill 1,000 enemies with critical hits (5,000 XP).
Brain Surgeon - Kill 2,500 enemies with critical hits (20,000 XP).
Relentless - Kill 5 enemies in succession with no more than 7 seconds between each kill (500 XP).
Chain Killer - Kill 10 enemies in succession with no more than 7 seconds between each kill (1,000 XP).
Killing Spree - Kill 15 enemies in succession with no more than 7 seconds between each kill (2,000 XP).
Conveyor of Death - Kill 5 enemies in succession with no more than 7 seconds between each kill (5,000 XP).
Action Hero - Kill 50 enemies using your Action Skills (1,000 XP).
Beware! Mad Skills! - Kill 250 enemies using your Action Skills (2,000 XP).
Why Do You Even Carry a Gun? - Kill 1,000 enemies using your Action Skills (5,000 XP).
Your Kung Fu is Best - Kill 2,500 enemies using your Action Skills (20,000 XP).
Seasoned Killer - Kill 500 enemies (1,000 XP).
Numb to the Voice - Kill 1,000 enemies (2,000 XP).
Terror of Pandora - Kill 4,000 enemies (5,000 XP).
I am Become Death... - Kill 10,000 enemies (20,000 XP).
Pocket Change - Earn $10,000 (1,000 XP).
Money, it Buys Happiness - Earn $250,000 (2,000 XP).
The Rich Get Richer - Earn $1,000,000 (5,000 XP).
How Much For the Planet? - Earn $9,999,999 (20,000 XP).
Duelist - Win 10 Duels (500 XP).
Smack Down! - Win 50 Duels (1,000 XP).
Bragging Rights - Win 250 Duels (2,000 XP).
Invincible - Win 1,000 Duels (5,000 XP).
What is That Thing? - Kill 50 Guardians (1,000 XP).
The Vault is Mine - Kill 250 Guardians (2,000 XP).
Prelates Relict - Kill 1,000 Guardians (5,000 XP).
Dominant Species - Kill 2,500 Guardians (20,000 XP).
Rakk Slayer - Kill 50 Rakk (1,000 XP).
It if Flies, it dies - Kill 250 Rakk (2,000 XP).
Rakk Flak - Kill 1,000 Rakk (5,000 XP).
If I Can't Fly, No One Flies - Kill 2,500 Rakk (20,000 XP).
Skag Slayer - Kill 50 Skags (1,000 XP).
SIT! STAY! PLAY DEAD! - Kill 250 Skags (2,000 XP).
I Hate Dogs - Kill 1,000 Skags (5,000 XP).
You Are The Skagpocalypse - Kill 2500 Skags (20,000 XP).
Spiderant Slayer - Kill 50 Spiderants (1,000 XP).
Bug Crusher - Kill 250 Spiderants (2,000 XP).
I Hate Bugs - Kill 1,000 Spiderants (5,000 XP).
The Exterminator - Kill 2,500 Spiderants (20,000 XP).
Spray and Prey - Get 50 kills with the combat rifle (1,000 XP).
Size Matters - Get 250 kills with the combat rifle (2,000 XP).
Make Chunks - Get 1,000 kills with the combat rifle (5,000 XP).
One Man Army - Get 2,500 kills with the combat rifle (20,000 XP).
Draw! - Get 50 kills with Pistols (1,000 XP).
Size Matters - Get 250 kills with Pistols (2,000 XP).
Make Chunks - Get 1,000 kills with Pistols (5,000 XP).
One Man Army - Get 2,500 kills with Pistols (20,000 XP).
Get Off My Lawn! - Get 50 kills with Shotguns (1,000 XP).
Taste the Red Mist - Get 250 kills with Shotguns (2,000 XP).
Instant Autopsy - Get 1,000 kills with Shotguns (5,000 XP).
Buckshot Legend - Get 2,500 kills with Shotguns (20,000 XP).
Boom - Get 50 kills with Launchers (1,000 XP).
BOOM - Get 250 kills with Launchers (2,000 XP).
KaBOOM! - Get 1,000 kills with Launchers (5,000 XP).
KABOOOOOOOOM!!!! - Get 2,500 kills with Launchers (20,000 XP).
One Shot, One Kill - Get 50 kills with Sniper Rifles (1,000 XP).
I'll Wait Back Here... - Get 250 kills with Sniper Rifles (2,000 XP).
Brain Ventilator - Get 1,000 kills with Sniper Rifles (5,000 XP).
Finger of God - Get 2,500 kills with Sniper Rifles (20,000 XP).
Road Rage - Get 50 kills with a vehicle (1,000 XP).
Vehicular Manslaughter - Get 250 kills with a vehicle (2,000 XP).
School Bus Driver - Get 1,000 kills with a vehicle (5,000 XP).
Hell on Wheels - Get 2,500 kills with a vehicle (20,000 XP).
Punchy - Get 50 kills with Melee attacks (1,000 XP).
Brawler - Get 250 kills with Melee attacks (2,000 XP).
Boxer - Get 1,000 kills with Melee attacks (5,000 XP).
Heavyweight Champion - Get 2,500 kills with Melee attacks (20,000 XP).
Hot! Too Hot! - Get 50 kills with Incendiary attacks (1,000 XP).
Toasty! - Get 250 kills with Incendiary attacks (2,000 XP).
Plays with matches - Get 1,000 kills with Incendiary attacks (5,000 XP).
Pyromaniac - Get 2,500 kills with Incendiary attacks (20,000 XP).
Zap! - Get 50 kills with Shock attacks (1,000 XP).
Nikola is a friend of mine - Get 250 kills with Shock attacks (2,000 XP).
Put forks in sockets - Get 1,000 kills with Shock attacks (5,000 XP).
Shocker - Get 2,500 kills with Shock attacks (20,000 XP).
Chemistry Rocks! - Get 50 kills with Corrosive attacks (1,000 XP).
Why is the floor all gooey? - Get 250 kills with Corrosive attacks (2,000 XP).
Mixes household chemicals - Get 1,000 kills with Corrosive attacks (5,000 XP).
Chemist - Get 2,500 kills with Corrosive attacks (20,000 XP).
Boom Goes the Dynamite! - Get 50 kills with Explosive attacks (1,000 XP).
Too Bad About the Tinnitus - Get 250 kills with Explosive attacks (2,000 XP).
Crosses Border for fireworks - Get 1,000 kills with Explosive attacks (5,000 XP).
Demolitionist - Get 2,500 kills with Explosive attacks (20,000 XP).
What's in Here? - Open 50 lootable objects (1,000 XP).
Scavenger - Open 250 lootable objects (2,000 XP).
Wilderness Survivor - Open 1,000 lootable objects (5,000 XP).
Cachet Lucres - Open 5,000 lootable objects (20,000 XP).
Ooo! Shiney! - Open 5 chests (1,000 XP).
Treasure Hunter - Open 25 chests (2,000 XP).
Swag Master - Open 100 chests (5,000 XP).
Envy of Pirates - Open 500 chests (25,000 XP).
How Much For the Gun? - Sell 50 items (1,000 XP).
Gun Runner - Sell 100 items (2,000 XP).
Arms Dealer - Sell 400 items (5,000 XP).
Merchant of Death - Sell 2,000 items (20,000 XP).
Impulse Buyer - Buy 5 items (1,000 XP).
Good Consumer - Buy 50 items (2,000 XP).
I Want it All! - Buy 200 items (5,000 XP).
Self-contained Economy - Buy 500 items (20,000 XP).
Lots of Shots - Shoot 2,000 times (1,000 XP).
Keep Firing - Shoot 10,000 times (2,000 XP).
Who Made That Man Gunner? - Shoot 25,000 times (5,000 XP).
I Fired Every Bullet Ever - Shoot 100,000 times (20,000 XP).
Hang Time - Get two seconds of vehicle hang time (500 XP).
Airborne - Get three seconds of vehicle hang time (1,000 XP).
This is Not a Flight Simulator - Get four seconds of vehicle hang time (2,000 XP).
Orbit Achieved - Get five seconds of vehicle hang time (5,000 XP).
12 Days of Pandora - Master the technology of Pandora (12 assault rifle kills, 11 pistol kills, 10 shotgun kills, 9 smg kills, 8 sniper rifle kills, 7 melee kills, 6 critical hit kills, 5 explosive kills, 4 shock kills, 3 incendiary kills, 2 face melted kills, and 1 grenade kill) (5,000 XP).