Let's talk about how experience points are awarded.

The Player's Handbooks states:

... as he or she completes adventures and returns to an established base of operations, the Dungeon Master will award experence points to the character for treasure gained and opponents captured or slain and for solving or overcoming problems through professional means. (Gygax, pg. 106; emphasis mine)

I want to draw your attention to a few points in that rather dense sentence.

• Experience points are awarded when a character completes an adventure. This implies that the DM is keeping a running tally of experience points earned during an adventure, which she will award at the completion of said adventure. However, the definition of "an adventure" isn't really spelled out here. More on that in a bit (see the Adventures and the Meta-Game post).

• Experience points are awarded when a character returns to an established base of operations. This is an important point. Much of original AD&D operates under the assumption that some sort of "Home Base" exists and is where PCs live/work/rest when not traveling and/or adventuring. Returning to this base of operation is an important trigger for Campaign and PC events, like the above awarding of experience points.

  Remember to inform your DM if you intend that your base of operations is moving, or has changed!

• Experience points are awarded for treasure gained. This is simply an award of 1 xp for each 1 gp. However, the Dungeon Master's Guide makes it clear that the xp awarded for gp is that treasure which was,

  ... physically taken out of the dungeon or lair and turned into a transportable medium or stored in the player's stronghold ... (Gygax, pg. 85).

  I interpret transportable medium to be the Fantasy RPG World's equivalent of "Cash"; ie. Gems, coins, or maybe even a marker from a bank.

  Also, I don't believe the intent of the word's "player's stronghold" was to infer that only those characters who own a literal stronghold have this options, only that the character has stored her treasure somewhere that provably belongs to her.

  Finally, the Dungeon Master's Guide also makes it clear that the xp earned from treasure is still awarded by the DM. The Players do not note on their character sheets that the xp was earned until the DM informs them of the total xp earned from the "adventure" (again, more on this later)). The DM will award a total xp amount, which the Player's are meant to assume includes both monsters slain and treasure gained xp combined.

  Caveat: If a significant disparity exists between the level of challenge of the encounter from which the treasure was gained and the experience level of the party, an adjustment to the awarded xp should be made.¹

• Experience points are awarded for opponents captured. My interpretation of the rules on this subject (xp for captured monsters/opponents is mentioned frequently, but the details are vague) are that captured opponents must be ransomed or sold to extract xp from them. This, in effect, turns captured foes into a type of treasure item, which would then use the rules (above) for generating xp from gp value.

• Experience points are awarded for opponents slain. This is the classic, everybody-knows-how-it-works-already, xp value of a monster being awarded to the PCs which participated in the battle to slay it. There are two caveats, and one exception.

  Exception: In the event of a true single-handed slaying, only that PC which slayed the monster will be awarded its xp value.

  Caveat: The Dungeon Master's Guide reads,

  ... a magic-user protected by fighters keeping off the enemy so he or she can cast spells which slay monsters is NOT fighting single-handed" (Gygax, pg. 85).

  Caveat: If a significant disparity exists between the level of challenge of the encounter and the experience level of the party, an adjustment to the awarded xp will be made.¹
  ¹This rule only ever applies when the level of challenge was below that of the experience level of the party. Ie. the party will be awarded full xp (never more) for a slain monster if its challenge level is equal to or above the experience level of the party, and some fraction of the xp if its challenge level is below the experience level of the party.

• Experience points are awarded for overcoming problems through professional means. Unfortunately, the Player's Handbook and the Dungeon Master's Guide seem to diverge slightly on this point.

  The Player's Handbook seems to indicate some kind of subjective award by the Dungeon Master for adhering to the framework of a Character's class during an adventure.

  The Dungeon Master's Guide also makes a similar point, but instead of awarding bonus xp for that adherance, it applies a penalty: when a Character is eligable to gain a level, each adventure in which the Character did not strictly adhere to the natural functions of his class will add extra time (and therefore cost) to the study/training required to achieve that level.

  I will use the rules in the Dungeon Master's Guide, but I have decided to also use the (implied) rule from the Player's Handbook as well. This will allow me to reward those Players utilizing their characters appropriately, as well as allow me to encourage the type and style of play I want emphasized in the game. We'll call this "bonus" xp. Many contemporary RPGs have similar mechanism named "Roleplaying XP", or "Storytelling XP", or the like.