This is not the first and certainly not the last attempt to systematize experience rewards for monster kills (or "monster subduals" for the merciful orc-lovers among you), and yet I dig Mr Lakofka's take [from Dragon #80] and believe it deserves a bit of show-casing here.
One of the Dungeon Master’s most important functions is to award experience points to the party after an adventure or an evening of play. To do this properly, one must reevaluate the chart on page 85 of the Dungeon Masters Guide [1st Edition].
When we look at the experience-point values for monsters given on page 85 of the DMG, we see that monsters are generally grouped in a pattern x+1 to y (e.g., 4+1 to 5). This pattern, however, does not properly reflect that a monster’s “to hit” probabilities change between 4+3 and 4+4. That is, a 4 HD monster hits on the same number as a 4+3 HD monster does, but a 4+4 HD monster hits as a 5 HD monster.
The rules on saving throws (page 79, DMG) specify that a 4 HD monster (one that is primarily a “fighter” type) saves as a 4th-level fighter, while one with 4+1 to 4+4 hit dice saves as a 5th-level fighter.
These two facts taken together mean that the experience-point award for a certain monster is based more upon that monster’'s saving throws than upon its ability to fight. That seems like backwards logic.
A simple solution would be to make the combat tables and the saving-throw matrix both progress in the same fashion; i.e., a 3+4 HD to 4+3 HD monster saves as a 4th level fighter, while a monster of 4+4 to 5+3 HD strikes 5% more often and saves as a 5th-level fighter.
If that becomes the rule, then designing a new chart for the experience-point value of monsters becomes an easy matter. Following the chart are lists of characteristics and abilities that should be classified as special or exceptional abilities. Many of the individual listings are taken directly from the DMG. Suggested additions and alterations are printed in italic type.
Typical Special Abilities
Three or more attacks per round; missile discharge; armor class 0 or lower; special attacks (blood drain, hug, crush, etc.); special defenses (regeneration; hit only by special and/or magic weapons of +1); high intelligence which actually affects combat; use of minor (basically defensive) spells; attack multiple opponents in the same round; immunity or resistance to a particular common attack form (fire, lightning, cold); using +1 armor (or any shield); using +1 weapon; using minor offensive/defensive magic item; ability to do more damage than like monsters (or characters) due to exceptional strength (but see below).
Typical Exceptional Abilities
Energy level drain; paralysis; poison; major breath weapon; magic resistance; spell use; swallowing whole; ability to cause weakness; attacks causing maximum damage greater than 20 singly, 24 doubly, 28 trebly or 32 in all combinations possible in 1 round; special purpose weapon; hit only by +2 or better weapon; using protection item (cloak, ring) of +1 to +3.
This new experience-point chart will give fair awards based on a monster’s ability to hit and damage plus its special and exceptional abilities. The awarding of experience points for killing character types (as NPCs) involves very complex calculations. Be sure to award extra experience for magic carried and employed and for the ability to cast more and more powerful spells (due to ability or carried magic); for instance, the spells of a wizard are much more potent than those of an enchanter, and assigning a double exceptional ability would be a good way to reflect this.