From Alpha Centauri Wiki
- All bases for each faction are ranked from top to bottom by Energy output.
- Bases are paired off from top to bottom. If one faction has more bases, these are ignored.
- For each pair of bases, sum the combined economic output and divide by eight, rounding up.
- Double this value if a Global Trade Pact is in effect.
- For each individual base, the commerce formula is as follows: (ValueFromStep4) × (CommerceTech + 1) ÷ (TotalCommerceTech + 1) .
- CommerceTech is the total number of economic technologies discovered, plus faction & Economy bonuses.
- TotalCommerceTech is the total number of economic technologies discovered by all factions.
- Now, using the value from step five, divide by two if no Pact (only a Treaty).
- Add one if Planetary Governor.
- Reduce to 0 if sanctions are in effect against either faction.