Should I give XP for non-antagonistic encounters?

1. What if my players encounter a bunch of centaurs (or other intelligent creatures such as orcs or men), get a reaction roll that indicates the centaurs are reluctant to fight, and the PCs leave after a brief and peaceful interaction before leaving. Should I give them XP for that encounter? 

 

2. Say my players instead encounter monsters or men who have a confrontational reaction to the PCs, wishing violence, but the PCs manage to de-escalate the situation and leave without bloodshed. Should I give them full monster XP for that? Is avoiding violence a reward in itself?

 

3. How about monsters or beastmen that demand a toll or other tribute from the PCs (as in Sakkara), but the party simply pays them and continues on their way? Is that kind of interaction worthy of XP?

XP from combat is a very small portion of XP that players will get relative to finding and returning treasure.  Any choice you make will not inherently unbalance the game as long as you don't have players that scheme to "encounter" the same foes multiple times.

 

That aside, most rulings I've seen on these forums suggest that leaving or resolving things amicably before fighting starts is not worth XP, but fighting and then, say, accepting a surrender or taking them alive would.

I personally give combat XP for any situation in which the encountered creatures:

-Begin the encounter at least thinking about fighting the PCs
-End the encounter with no interest in fighting them ever.

Whether this is accomplished through diplomacy or killing them all, I leave up to the PCs. So I would not give them XP for paying a single tribute, but I would give them XP if they paid so much tribute that the bandits retired and left them alone forever. Similarly, if they just escape, no XP; but if they escape in a fashion that deals with the enemies in a permanent fashion (perhaps the enemies were conjured creatures and will only be around for a day, and they successfully hide from them until they disappear), I would give them XP. I do not give XP for congenial conversations with friendly-ish creatures, but if they wanted to fight and then got talked out of it, I’d give that XP (as long as it was a ‘you don’t want to ever fight us’ convincing instead of a ‘come on let off with a warning this time’ convincing.)

(edit: I am not an Autarch, this is just how I do it myself.)

Personally, I wouldn't give XP for it. The advantage of not fighting is not spending HP or other resources; getting XP out of the fight is a consolation prize. "Sorry you didn't manage to get gold without any PCs losing an arm. but at least you get a little bonus XP!"
 

I generally grant XP along the same broad guidelines as Aryxymaraki describes.

One of the things that I LOVE about OSR in contrast to 3E is that "winning" doesn't necessarily mean 100% destruction of the enemy. I see XP as a carrot for preferred behavior, and I definitely prefer the PCs to come up with creative solutions that don't involve combat. Moreover, combat is often boring, or at least less interesting than cunning diplomacy; if I can incentivize a course of action that doesn't involve spending our most precious player resource (time), it's a win in my book. My approach may not be "right" or "correct," but it favors the playstyle I personally like to see at the table.

Jard points out a critical point, though: Regardless of your ruling, combat XP should be a pretty small part of overall XP earned. Whatever you choose to do, it won't break the game.

I, likewise, rule pretty much as do Aryxymaraki and Hardrada. I wouldn't want the PCs to get XP for every friendly encounter as they could level up by having a tickertape parade. But I wouldn't want to penalize PCs for, e.g., persuading the monsters to work for them instead of fight them.  

 

My take is that convincing a group of monsters to join you is its own reward. 

Generally, I only give XP for monsters that are opposed and "defeated," and I deliberately resist any attempts by my players to corner me into some kind of IF-THEN-ELSE matrix regarding what might constitute "defeating" a monster, other than the obvious.

I genuinely believe that outsmarting or out-talking an opponent should be worth full XP in many circumstances, but I also know my players well enough to know that a few of them will begin designing an industrial XP farming operation the moment I codify the precise rules that separate an encounter which grants XP from one that does not.

I started out doing something like the majority of the approaches above, but more lately I've switched around to being much more lenient. At this point, my standard is to consider what would happen if the PCs were to

1) roll the worst possible results (i.e. a modified 2- on reaction, the party being fully surprised, etc) during the encounter, and

2) did absolutely nothing to attempt to avoid hostilities.

If this scenario would result in a fight or any other negative outcome, but that didn't happen due to a party-member action or ability, then I assume that the encounter was "defeated". Avoiding the fight gives full experience as if it were won. That includes using evasion, stealth, deception, diplomatic manipulation, barrier spells, fear, illusions, whatever.

Since the majority of experience comes from treasure, this doesn't have a large effect on leveling rate (avoiding fights has provided less than 5% of all experience in my campaign, I'm quite sure). Maybe if players actually start trying to ticker-tape their way to the next level, I'll change my mind, but so far it's a distant hypothetical.

Bear in mind that this reflects my campaign structure, where players level up only once every 12 sessions or so. At a session a month that amounts to gaining only one level a year, so I still feel really stingy compared to pretty much every other campaign being run in my gaming group. I can afford to be more generous. Not saying everyone else should do the same thing, just that it's worked well for me.

The only thing that worries me slightly is that the party might double dip by coming back to avoid enemies (or just kill them) after already avoiding them once. I generally wouldn't allow that if the players choose to do it voluntarily, although I probably would if it were outside their control, like a recurring villain. Batman deserves exp every time he takes down the Joker, not just the first time!