Player's Handbook[]
A character with endurance proficiency is able to perform continual strenuous physical activity for twice as long as a normal character before becoming subject to the effects of fatigue and exhaustion. In those cases where extreme endurance is required, a successful proficiency check must be made. Note that this proficiency does not enable a character to extend the length of time that he can remain unaffected by a lack of food or water.
Player's Option: Skills & Powers[]
Endurance: A character with this proficiency can perform continual strenuous physical activity for twice as long as a normal character before becoming exhausted. If the character is ever required to make a Strength/Stamina check or a Constitution/Fitness check, the character can add his endurance score to his success number. If the fatigue rules from the Player's Option: Combat & Tactics book are in play, the endurance proficiency is treated differently (see Combat & Tactics, Chapter One).
The Complete Thief's Handbook[]
Recommended: Thug.
This proficiency is normally restricted to warriors. Its description is on p. 58 of the Player's Handbook.
The Complete Book of Dwarves[]
A hardy and resilient race, dwarves automatically gain the Endurance proficiency (see the Player's Handbook, page 58) at no cost.
Campaign Option: Council of Wyrms Setting[]
Endurance allows strenuous activity to be maintained for twice as long as normal. Tasks requiring extreme endurance require a proficiency check. The proficiency does not counter the effects of starvation or thirst, but it does increase flying distances.
Hatchlings can't select this proficiency.