Psionic Ability or PSI is one of the basic statistics in System Shock 2.


The maximum effective Psionic Ability level is 10, although most Psionic skills benefit from a PSI up to 8. The player can only permanently upgrade Psionic Ability to level 6, while the next two levels require a combination of the following items/Psionic Disciplines:

Overloading a Psi Power casts it with a bonus of +2, to a maximum effective PSI of 10 (player needs to have PSI 8 already before casting to reach PSI 10). It is not possible to reach PSI 9 or 10 without Overloading.

Psionic Ability increases the Psi Points of the player and influences the duration/effectiveness of Psionic Disciplines. The amount of bonus Psi Points given depends on the difficulty:

Psionic Ability vs maximum Psi Points Table

Psionic Ability Level Easy Normal Hard Impossible
1 26 15 11 6
2 42 25 19 11
3 58 35 27 16
4 74 45 35 21
5 90 55 43 26
6 106 65 51 31
  • Maximum Psi Points of the player change when upgrading the PSI stat, but they are not affected in any way by the items, RPA, nor overloading.
  • The only other thing affecting the player's maximum Psi Points is unlocking main Tiers of Psi Powers. Each Tier adds to the max Psi Points a value of 2x the level of the Tier (no matter the skill level), e.g. Tier 3 adds 6 to the max Psi Points. The total bonus to max Psi Points is thus 30.

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