A list of events that occurred on April 18 related to Six Flags.

• 1986 – Six Flags St. Louis opens for the 1986 season with the all-new Colossus Ferris wheel.
• 1998 – 23 riders on the Demon roller coaster at Six Flags Great America are stranded upside-down in the middle of the ride's second vertical loop. Firefighters used a cherry picker to bring riders to safety, although some were on the ride for as long as three hours. The incident was the result of a mechanical failure.
• 2008 – Goliath opens at Six Flags Fiesta Texas.