Dice Pool

A dice pool is when you are rolling a different number of dice for each situation. Usually the # of dice depends on one or more properties of the actor. The classic example is adding Dexterity of 3 to Pistols Skill of 2 to roll 5 dice.

Determining success or failure is usually done in one of three ways:

• Additive Sum the values of all the dice rolled. Used in Shadowrun, West End Games's Star Wars D6. White Wolf's Trinity and Exalted also use this system, where any die showing less than 7 counts as "0", 7-9 counts as "1" and 10 counts as "2." Some games come with special dice that have a 'success' colour on some sides with the others blank.
• Target Number The GM sets a number for the difficulty of the circumstance; any dice rolled below that number count as "0", any dice above that count as "1". This method is used for White Wolf Games's Storyteller system. It's often criticized because few people (game designers notwithstanding) understand when it's appropriate to modify the number of dice or to modify the difficulty number.
• Highest Die Only use the highest value showing on the dice rolled. In contests, compare each actor's highest die, and in case of ties compare their 2nd highest dice, then third, and so on, with absent dice as automatic losses. This system is used in Dream Pod 9's Heavy Gear, Task Force Games's Prime Directive, and Donjon. When two opponents are using dice of the same size, with pools of the same size, the odds are always 50/50.

One Roll Engine uses something really weird, and has it's own page.

Common variants are:

• exploding dice that show the highest value.
• dice showing their lowest face are counted as a negative value.
• dice showing their lowest face, in the absence of any successes, shows a critical failure.
• changing the size of the dice for actors that are superior/inferior to each other.
• being able to set one or more dice to a desired facing before or after rolling, usually to represent automatic successes granted by supernatural ability.

Examples

• Shadowrun is considered by some to be the granddaddy of dice-pool RPGs, and uses d6. Older editions used Target Number; 4th ed uses a simple Additive pool (1-4 = 0; 5-6 = 1).
• Inquisitor If a player was trying to perform a dangerous action as part of his turn (all actions had to be declared before the player checked to see how many were successful) he was obliged to then roll less 1's than 6's otherwise he would fumble the action, often with humorous results (guns exploding, premature detonation, setting off alarms or falling to their death were common fates for characters who failed.)
• World of Darkness uses d10 and variable target numbers and exploding 10s.
• Exalted uses Additive d10s with '7' as the target number (1-6 = 0; 7-9 = 1; 10 = 2).
• Donjon uses Highest Die d20s.