Old Faithful area of Yellowstone National Park, also known as the Upper Geyser Basin, is the largest concentration of geysers in the world.

Old Faithful erupts more frequently than any of the other big geysers, although it is not the largest active or most regular geyser in the park. Its average interval between eruptions is about 76 minutes, varying from 45 - 110 minutes. An eruption lasts 1 1/2 to 5 minutes, expels 3,700 - 8,400 gallons (14,000 - 32,000 liters) of boiling water, and reaches heights of 106 - 184 feet (30 - 55m). It was named for its consistent performance by members of the Washburn Expedition in 1870. Although its average interval has lengthened through the years (due to earthquakes and vandalism), Old Faithful is still as spectacular and predictable as it was a century ago.

Plume Geyser erupts about every 20 minutes. Its 3 - 5 quick bursts can reach heights of 25 ft (8m). This is a relatively young geyser that came into existence when a steam explosion created its vent in 1922.

An eruption of Grand Geyser, the tallest predictable geyser in the world, occurs every 7 - 15 hours. A classic fountain geyser, Grand erupts from a large pool with powerful bursts rather than a steady column like Old Faithful. An average eruption lasts 9 - 12 minutes and consists of 1 - 4 bursts, sometimes reaching 200 feet (60m).

Castle Geyser has the largest cone and may be the oldest of all geysers in the basin. Its eruption pattern has changed considerably throughout its recorded history. Castle is currently erupting about every 10 - 12 hours. A water eruption frequently reaches 90 feet (27m) and lasts about 20 minutes. The water phase is followed by a noisy steam phase lasting 30 - 40 minutes.

Giant Geyser was dormant for many years after the energy shift in 1955. Since then, it has slowly become active again. During 1997, its eruptions occurred every 3 - 10 days. This spectacular geyser's eruptions last about an hour and can reach heights of 180 - 250 feet (55 - 76m). During eruptions small geysers nearby may also erupt.