A-0 Geyser is a geyser in the Lower Geyser Basin of Yellowstone National Park in the United States.
A-0 Geyser is part of the White Creek Group which includes Spindle Geyser and Botryoidal Spring. It can be identified by its shallow, round basin with a round vent in the middle found 100 feet (30 m) southeast of the Surprise Pool parking area. It erupts for a duration of 30 to 40 seconds with an interval of around 24 minutes between eruptions.
The fountain reaches a height of 5 to 10 feet (1.5 to 3.0 m).
The name A-0 is an unofficial name based on the proximity of this geyser to the dormant A-1 and A-2 geysers.