Old Faithful is undoubtedly the world's best-known geyser and most publicized natural phenomenon of any sort. It is one of the most predictable geysers in all of Yellowstone Park. Its heights, intervals and lengths of eruption are constantly changing and evolving due to ongoing processes within its 'plumbing' and from earthquakes.

Old Faithful has two types of eruption patterns - short ones that last 1 1/2 to 2 minutes, and long ones that last 3 to 5 minutes. The eruption heights vary from 106 feet to 184 feet, with an average of 130 feet, and discharges of up to 8,400 gallons of water per eruption. The geyser's average interval between eruptions is currently about 92 minutes.