Every Dark Gyarados card we price, most valuable first. Prices are what copies actually sold for, updated daily.
The same Pokemon is also printed as Gyarados and Misty's Gyarados, priced separately because the game treats them as different cards.
What a Dark Gyarados card is worth
The most valuable Dark Gyarados on this list is Dark Gyarados from EX Team Rocket Returns at $315£237.08€277.41, and the 5 priced copies across 4 sets are worth $610£459€537 together. Most of that sits in a handful of printings: the older the set and the scarcer the print run, the wider the gap to the rest.
Dark Gyarados is printed in Japanese as well: 3 cards across 3 sets, the most valuable of them Dark Gyarados from Rocket Gang at $41.76£31.43€36.78. Switch the list above to Japanese to read those, or to Both to rank the two catalogues against each other.
The highest PSA 10 on record for Dark Gyarados sold for $8,939£6,728€7,872. 1st Edition and reverse holo printings are priced separately from the standard card, because they do not trade at the same money.
If you are trying to identify which Dark Gyarados you have, the set name is printed on the card and the collector number sits in the bottom corner. Open the card here and the page carries every printing of it, the graded prices, and whether grading the copy is worth the fee. Sets to start with: EX Team Rocket Returns, Team Rocket, WoTC Promo.