Alien Appearance Ratios

December (1998) - January
Mission/Race	Sectoid	Snakeman	Ethereal	Muton	Floater
Alien Research	70%	10%	-	-	20%
Alien Harvest	50%	20%	-	-	30%
Alien Abduction	60%	-	-	-	40%
Alien Infiltration	60%	20%	-	-	20%
Alien Base	30%	20%	-	-	50%
Alien Terror	30%	-	-	-	70%
Alien Retaliation	60%	20%	-	-	20%

February - March
Mission/Race	Sectoid	Snakeman	Ethereal	Muton	Floater
Alien Research	60%	10%	-	-	30%
Alien Harvest	50%	-	-	-	50%
Alien Abduction	40%	-	-	-	60%
Alien Infiltration	50%	20%	-	-	30%
Alien Base	40%	20%	-	-	40%
Alien Terror	60%	-	-	-	40%
Alien Retaliation	30%	30%	-	-	40%

April - May
Mission/Race	Sectoid	Snakeman	Ethereal	Muton	Floater
Alien Research	30%	10%	-	30%	30%
Alien Harvest	30%	-	-	30%	40%
Alien Abduction	50%	-	-	-	50%
Alien Infiltration	20%	20%	-	50%	10%
Alien Base	10%	40%	-	30%	20%
Alien Terror	20%	60%	-	-	20%
Alien Retaliation	20%	20%	-	40%	20%

June - July
Mission/Race	Sectoid	Snakeman	Ethereal	Muton	Floater
Alien Research	20%	10%	-	40%	30%
Alien Harvest	10%	-	-	40%	50%
Alien Abduction	30%	-	-	-	70%
Alien Infiltration	10%	10%	40%	30%	10%
Alien Base	10%	40%	10%	20%	20%
Alien Terror	10%	20%	40%	20%	10%
Alien Retaliation	20%	20%	20%	20%	20%

August and Beyond
Mission/Race	Sectoid	Snakeman	Ethereal	Muton	Floater
Alien Research	30%	10%	-	30%	30%
Alien Harvest	30%	-	-	30%	40%
Alien Abduction	50%	-	-	-	50%
Alien Infiltration	20%	20%	10%	40%	10%
Alien Base	10%	20%	40%	20%	10%
Alien Terror	20%	30%	20%	20%	10%
Alien Retaliation	10%	10%	40%	20%	20%

Notes

• The first appearance rate block includes December 1998, however the game starts in January 1999. It is included because the tables cover 2 month blocks.

• All months beyond August 1999 use the August table.

• All Retaliation rows are unused. Retaliation missions are generated in response to shooting down enemy craft, with a set probability that is scaled by the difficulty level multiplier.

• All values listed above are interpreted off probability tables obtained directly from GEOSCAPE.EXE.

• The crew of already established Alien Bases, ships on Alien Supply missions, and Terror Sites will be crewed by the same crew that founded the base or terror site, and are not affected by these tables.

• Creation of alien bases are the end result of a successful Alien Base mission. They also have a very high probability of appearing at the end of an infiltration mission, often corresponding with the withdrawal of a funding nation.

• The Cydonia mission has a pre-defined crew setup.