Operational Reserves
Operational Reserves (development) in the Stellaris encyclopedia: The Operational Reserves for Nomadic Empires are a combined view of Minerals and Energy Credits.
Operational Reserves in the game's words
The encyclopedia entry as the game shows it in its tooltips; underlined words open their own entry or page here.
The Operational Reserves for 
Nomadic Empires are a combined view of 
Minerals and 
Energy Credits.
There is still income and upkeep of Minerals and Energy Credits, but managed as a Situation.
One point of Operational Reserves is equal to one Mineral or one Energy Credit.
Operational Reserve Capacity has a base value of $@nomad_reserves_base|0$.
Each Arkship we own increases it by:
- Tier I: $@nomad_reserves_per_tier_1|0$
- Tier II: $@nomad_reserves_per_tier_2|0$
- Tier III: $@nomad_reserves_per_tier_3|0$
Civilian Arkships grant an additional $@nomad_reserves_civilian_per_tier_1|0$ per Tier.
The Stages of the situation affect the empire's 
Arkships in different ways, and Approaches can be selected to conserve resources or burn through them for higher productivity.
Minerals and Energy Credits can be bought on the 
Market, but not sold.
More in Development
Source: common/game_concepts (concept_operational_reserves) and localisation/english, Stellaris Cygnus v4.5.2 (9776).