Adrenaline

Certain Warrior skills are fueled by adrenaline rather than Energy. It is gradually built up each time the Warrior hits or is struck in combat, each such blow being added to the characters adrenaline level. Some skills increase the rate of adrenaline build up, while others expend it entirely.

Adrenaline Points
Adrenaline is not actually gained in strikes, but in points. Every adrenaline skill stores its own adrenaline points displayed by rising flames from 0 till fully charged. See this table for approximate number of adrenaline points needed for skills.

1Sever Artery and Counter Blow are 4 strike skills, but they actually need about 100 adrenaline points. The "points needed" row increases linear, the "adrenaline strikes" numbers are a simplification.

Gaining adrenaline
You gain 25 adrenaline points for every of your atacks that hits and you gain 1 point of adrenaline for every 1% health lost from your maximum. Note that this includes ranged attacks and excludes health degeneration. Commonly 4 strike skills are charged in about 3 hits time, because you take some damage at the same time. Gaining adrenaline means every adrenaline skill in your bar gains that much points.
 * Soothing Images sets all adrenaline gain to 0.

Using adrenaline
You can only use adrenaline skills that are fully charged with adrenaline. They cost 0 Energy. When you use an adrenaline skill all adrenaline skills in your bar lose 25 points, you should just get them back with your next hit, caused by the used adrenaline attack, or by taking as much damage as 25% of your maximum health.

Losing adrenaline
Losing adrenaline means every adrenaline skill in your bar loses that much points. You lose all adrenaline after you do not take any damage and do not attack for 20 seconds.
 * Some skills cause "...lose all adrenaline".
 * Sympathetic Visage causes a loss of adrenaline on a hit.

Skills that boost adrenaline

 * With Berserker Stance you gain 31.25 points every time you hit in melee (instead of 25).
 * With "For Great Justice!" all your adrenaline gain is amplified by 150% (the gain is not doubled as the description would suggest).
 * With Battle Rage you gain 50 points every time you attack.
 * With "To the Limit!" you gain 25 points for each foe in the area (max 25...125).
 * With Wary Stance you gain 25 points every time you block an attack skill.
 * With Ferocious Strike you gain ? points if your pet hits.
 * With Balthazar's Spirit you gain +2...5 points every time you take damage.
 * With Dark Fury you gain +25 points if you hit.

Reference
Research done by Ensign and Silmor. Original GW Guru thread.