This is how I distribute XP to my PC's. I thought I'd share it with you in case someone is a bit unsure and can use this as a template
Now I lead my group of PC's through a narrative and long campaign which does not include any pre-written scenarios, which has lead me to put up this list.
1 Session (8hours) = 150-225xp depending on how they generally perform (this includes narrative travel, shooting regular baddies and so on, the neutral state of play)
Minor Boss Encounter = 35-75xp depending on how dangerous etc
Medium Boss Encounter = 75-125xp depending on how dangerous etc
Major Boss Encounter = 125-250xp depending on how dangerous etc
Insane Boss Encounter = 250-500xp depending on how dangerous etc
Victorious Arch Nemesis Encounter = 500-1000xp depending on how dangerous etc
All boss encounters include all stages, meaning; if it's a Major Boss encounter which includes 2 minor bosses they do not gain extra XP for the minor ones, they gain xp for the whole encounter not individual bosses.
Complete an Encounter = 15-75xp an encounter is a pre-planned event which pits the PC's against foes, a difficult obstacle etc
Complete an Act = 750-1500xp
An act stretches across several sessions and contains multiple encounters and ends with a Boss Encounter, an act can contain several of the various boss encounters.
I have no set amount of sessions for each Act, it depends on the players how well they solve the various encounters they face.
Completed a Story Arc = 1500-2000xp A story arc is built of several Acts and ends with an Arch Nemesis Encounter
Good Role Playing = 25-75xp did they chat alot in character amongst themselves during the session? Did they act according to their characters upon facing problems?
Cinematic Stunts = 25-50xp Did someone leap over a chasm, grabbed the rope which was hanging in the middle of the chasm and swung to the other side to activate the bridge?
Web Of Mysteries = 25xp per player and additional 25xp for the person who solved the mystery. The Web Of Mysteries is my own term for solving riddles and questions I have plotted into their campaign. An example would be to unveil the true identity of a person, sticking a name with a face and moving onwards in the larger picture.
Achieve a PC goal 25-75xp: If the player successfully achieve a goal he has put for his character, such as getting his dirty little hands on a bolt gun or learning forbidden lore etc, the player gets a reward for pursuing his goal and complete it.
Bribe the GM: 5-10xp Bring the GM cookies and he shall reward you. I am not more but a man Emperor save me.
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This is how I distribute XP, feel free to use it as it is or as a template.
On an average my players gain somewhere between 250-400 xp / session, the highest anyone of them has got so far is 550xp but that was exceptional. They are now approaching level 4 with some 5-6 sessions behind them. (I have just recently begun to use this method of giving them xp so I have not been consistent in the past). And are approaching the end of an Act which will put them on The Valiant Star, a 1.5km long Trade Ship fighting through throngs of cultists as they chase the heretic Mechanicus Priest Belim Joz.