to get to level 20 really quickly simply play the mission 'Aquarium' (or sumin along those lines) in a private single player custom match, security, as a medic on easy difficulty and heal everybody..... if you do it properly you should get around 8 - 10,000 xp each time, maybe more...

lol thx for the tip, but i get 8-10k xp in any non-competition game as a medic as is..

There's some better methods out there. One is on the Reactor as Resistance. Set up the match as a private freeplay on stopwatch with 30mins as the length with minimum players set to one. Then start the round as any class aside from Operative, run into the vent room, go up the stairs and hide just inside that hallway leading to the bridge you can repair. Set your objective to "guard the vents" and let it sit for 30 minutes. You get 75 pts for the objective every few seconds which lets you rack up around 22k xp without even having to stay at the game.

The one with the highest xp I've seen can only be done with a buddy, but can net around 55-60k in 30 mins. It's on the same map as above, same settings, it'll be you vs your friend. The farming can start in the second part where you have to plant the bomb. So whoever is Resistance should go hack the vents, and Security can guard or run around building mg nests/capturing command posts while the vent is hacked.

In the second part the Resistance needs to go Soldier and Security needs to go Engineer. Meet at the reactor core, and have the Soldier place an HE charge while the Engineer places a turret pointing out the door. Once both are up the Soldier needs to shoot the turret but not destroy it, just damage it while the Engineer needs to disarm the charge. Then switch and have the Soldier place another charge while the Engineer repairs the turret; just rinse and repeat. I've only tried this one once, and it is rather boring. Also keep in mind the Engineer is the one that gets the insane amount of xp, the Soldier will only rack up about half as much.

But just like HK_Obayda said, you can still get a large amount of xp playing regularly as long as you're generous with buffs and work as a team. Plus playing with others is usually more enjoyable than just farming xp.

True, but playing with others while maxed out imo is even more fun, since you can play the game as it was meant to be played .

Wanna level up fast, Heres the best way.

Get a objective who has homing beacon. Get in disguise on a heavy because their more easier to identify. Get in a corner near the enemies spawn with a high elevation of view. Then all you do is hold L1 and spot them as they come out, then after a few seconds, look back to the ones who were spotted and spot them again, then repeat on everyone you see. Do this right and you should rack up around 15k-30k per game.

P.S. Works better with a sniper.