WKRG-TV reports a robbery appears to have been planned in advance.
The robbers cut off the electricity to the service station before going inside.
Prichard Police Chief Jimmie Gardner says the two clerks and three patrons inside the station were plunged into darkness when the armed men entered.
They made the patrons get down and then shot one clerk in the chest, killing him, and the other in the leg.
Their names have not been released.
Gardner says the robbers knew what they were doing.
The power box used to shut off lights in the service station is located about 35 feet away behind a car wash.