In 1991, X-Men #1 sold an estimated 8,186,500 copies, making it a likely contender for the best-selling single-issue comic book in history. And yes, that wiggle room matters. When it comes to determining the exact rundown of the best-selling comics of all time, the data is murky.

There are decades of comics history where industry number-crunchers only counted how many issues of Superman and Captain America newsstands ordered, leaving historians with only hard sales numbers from 1997 onward. And that’s without considering the apples to oranges comparison of America’s single issues method of distribution to, say, Japan’s doorstop-like weekly anthology magazines.

If you want to base everything on confirmed numbers, you’ve got to throw in quite a few caveats. You wind up with a list more like “The 10 best-selling American single-issue comic books of all time that we have hard data on.”

So that’s what we did.

Our research owes a lot to Comichron’s detailed compilations of the categories of best-selling comics; the site’s post about the difficulties of naming the “best-selling comics ever” is good and edifying reading. We also owe a grudging debt to Diamond Comics distributors, for the company’s monopolistic takeover of the American comic book shipping market, and its regular reporting of comic book pre-order sales ever since.

With that in mind, here are the 10 best-selling American single-issue comic books, according to the most concrete numbers in the industry’s spotty history.

10. Action Comics #1000 (2018)

Copies sold: 504,200

Rounding out the bottom of our list are the two youngest comics on it, this one commemorating the 80th anniversary of the first superhero and the second oldest continually running superhero comic still on stands today: Superman, and Action Comics. Action Comics #1000 is the first example of a trend we’ll see in the rest of the list, that is, the big anniversary blowout issue.

DC Comics printed the 80-page giant with 11 different covers, which is par for the course with a book of its magnitude and era. Aside from the milestone in comics history it represented, and the wealth of creators DC was able to attract to fill its anthology, Action Comics #1000 had a few other perks to attract the interested collector.

Superman returned to his classic costume in the issue — with his underwear on the outside — for the first time in seven years, and the issue also contained the first few pages of Brian Bendis’ run on Superman, a big turn around for the legendary Marvel Comics creator.

9. Detective Comics #1000 (2019)

Copies sold: 526,941

A year later (thanks to only a little bit of editorial shuffling of issue numbers) Batman got his own 80th birthday present, with Detective Comics #1000, for the first four-digit issue of the actual oldest still-running comic series.

Second verse, same as the first: The issue was an 80-page giant packed with a who’s who list of Batman writers and artists. But it couldn’t claim the clout of a long-time Marvel Comics writer’s first DC Comics work in years, or a costume change, to sweeten the deal.

How to account for the book selling 22 thousand more issues than Action Comics #1000? Likely, Batman is just more popular.

8. Amazing Spider-Man #583 (2009)

Copies sold: 530,500

Have you already figured out why an otherwise unremarkable issue of Mark Waid and Barry Kitson’s Amazing Spider-Man made it on this list? I’ll give you a hint: it was published on January 15, 2009.

But you’ve probably already guessed. It was all about the issue’s presidential tie-in story and variant cover, released to coincide with the inauguration of Barack Obama as the 44th president of the United States. The issue itself contained the backup story “Spidey Meets the President,” in which the Chameleon uses his skills at mimicry to try and take then-Senator Obama’s place and be sworn in as President.

Peter Parker is on hand covering the inauguration as a Daily Bugle photographer, and, as Spider-Man, he ferrets out the real Obama from the Chameleon by asking him a question only the real Barack Obama could answer: what was his nickname on his high school varsity basketball team? Over 530 thousand issues later, Amazing Spider-Man #853 made this list.

7. Secret Wars #1 (2015)

Copies sold: 550,500

2015’s Secret Wars was a follow up to one of the earliest and most notorious Marvel Comics crossovers of all time, 1984’s Secret Wars.

That story featured the cosmic entity the Beyonder zapping all of Marvel’s most popular heroes and villains to an alien planet where he forced them to fight to the death. The 2015 version continued the “Everyone is here!” vibe by destroying the Marvel multiverse. Leftover pieces of all the Marvel parallel Earths were collected into one patchwork planet called Battleworld, and things proceeded from there.

The crossover’s promise to destroy the long-standing Ultimate Marvel setting and end a 15-year era may have propelled sales. Or ... it may have been the more than four dozen variant covers.

6. Amazing Spider-Man #1 (2014)

Copies sold: 559,200

Smack in the middle of writer Dan Slott’s now legendary Spider-Man run, Amazing Spider-Man #1 was a happy turning point for the character. A few years earlier, Peter Parker lost control of himself when Doctor Octopus freaky-Fridayed himself into the wall-crawler’s body. Peter seemingly died in Otto Octavius’ ailing form, and his last wish moved Otto himself to renounce villainy and fight crime as the Superior Spider-Man.

But with Amazing Spider-Man #1 (actually the third Amazing Spider-Man #1 Marvel has ever published), Peter Parker was back in control of his own body — and Spider-Man — for the first time in two years.

Like others on this list, the issue was an anthology, with some big names in Spider-Man history returning to the character. It’s also the first issue of an ongoing series — making it a potential seller on the collectibles market. All of these factors may have contributed to its sell-out quality.

The nearly 75 variant covers probably didn’t hurt either.

5. FCBD Edition Ultimate Spider-Man #1 (2002)

Copies sold: 631,990

Ultimate Spider-Man #1 is something of an odd one out. It’s not a big anniversary issue, it’s not an anthology, and it arrived with a modest four variant covers.

What Ultimate Spider-Man is, in hindsight, is the beginning of a series that would spell massive changes for Marvel Comics. First, by marking the beginning of the rise of writer Brian Michael Bendis, and second, by eventually creating the circumstances under which Miles Morales would become Spider-Man.

But we’re not just talking about Ultimate Spider-Man #1, released in the year 2000. We’re also talking about the book’s 2002 Free Comic Book Day re-release, timed to coincide with the US premiere of Sam Raimi’s Spider-Man. The issue was designed to be a natural jumping on point for new readers, by restarting Peter Parker’s superhero story over from the beginning and modernizing it as it went.

That Hollywood draw of potential new readers propelled retailer preorders of the reissue, bolstering the overall sales numbers of Ultimate Spider-Man #1. It’s likely the book’s actual sales numbers are slightly higher, as the data we have on it does not include any reorders retailers may have made past that initial sales cutoff.

4. Batman: The 10-cent Adventure (2002) #1

Copies sold: 702,126

I can tell you firsthand that Batman: The 10-cent Adventure succeeded in its goal of grabbing readers with a nostalgically low price point because it’s the comic that convinced me to start buying comics. I had to find out what happened next, and I had to find out now.

The 10-cent Adventure kicked off the two part crossover arc Bruce Wayne: Murderer? and Bruce Wayne: Fugitive — which made our list of the best Batman comics ever made — and ended with a doozy of a cliffhanger. Bruce Wayne had been framed for murder, and the only way to get out of it was to admit his secret alibi: He’d been miles away as Batman at the time of death.

But a cliffhanger can’t sell a comic before it hits stands. The 10 Cent Adventure’s promotional price point (that is, 10 red pennies) probably had more to do with it.

3. Fantastic Four #60 (2002)

Copies sold: 752,699

Fantastic Four #60 combines the appeal of The 10-cent Adventure and Amazing Spider-Man #1. The issue isn’t the first in its series, but it did mark the beginning of a new era, with writer Mark Waid stepping for what would become an acclaimed three year run on the title.

The issue isn’t an anthology, but it did have a special promotional edition that sold for a mere nine cents — half a year after DC’s one-cent-more-expensive promotional stunt. As you can see, the issue makes sure to let you know that this edition is the “world’s cheapest comic magazine.”

2. Star Wars #1 (2015)

Copies sold: 1,073,000

If you’ve been paying attention to sales numbers, your eyes probably got wide. It’s a big jump from Fantastic Four #60’s 752,699 copies and Star Wars #1’s just over one million.

For that, we can look to the state of Star Wars in 2015. The anticipation of a new dawn for the franchise with Star Wars: The Force Awakens collided with a fandom adrift after the majority of its canon was declared defunct. Suddenly there were lots of gaps to fill in the Star Wars saga, and Marvel Comics was there to fill them, having recently repossessed the Star Wars comics license from its parent company Disney after Lucasfilm’s contract with Dark Horse Comics lapsed.

As a book telling canonical stories in the middle of the original Star Wars trilogy, Star Wars #1 hit that sweet spot of appealing to fans nostalgic for the old expanded universe and promising to show readers something new.

But that’s not the only factor at work here. The issue also had nearly 100 different variant covers to collect, and subscription box service Loot Crate also placed a hefty order of the comic, packaging a copy of Star Wars #1 in every box of its monthly shipment. Still, according to Comichron, Loot Crate only purchased a mere “several hundred thousand” copies — even if those orders don’t count, Star Wars #1 won’t be dethroned from the spot of best selling comic of the 21st century anytime soon.

1. X-Men #1 (1991)

Copies sold: 8,186,500

And finally, the granddaddy of them all: X-Men #1, famous for being the best selling comic ever that we have hard data on, with close to eight times more issues sold than its 2nd place challenger.

There has never been anything like the early ’90s in American comics since the early ’90s, and that’s for many disparate reasons. But the most relevant one here is what’s known as the Speculator Boom. With the mainstream eye on comic book collecting, thanks to the success of films like Batman and books like The Dark Knight Returns, news outlets started reporting on comics form the juiciest angle they could find: How much you could sell your old comics for.

The lure of finding a copy of Action Comics #1 and turning it around for over a million dollars gripped many people, and comics companies played into it, hyping big events — new costumes, first appearances, character deaths, and first issues — as not just narratively exciting but literally valuable.

Of course, the value in issues like Action Comics #1 and Amazing Fantasy #15 is that nobody knew that Superman and Spider-Man were going to be hits, and so almost nobody went to the trouble of producing, buying, or preserving many copies of their first appearances. Those books are rare, and therefore are considered valuable.

And that’s what everybody thought was gong to happen with X-Men #1, which shipped in staggered installments over five weeks, with five different covers. Four of the covers, if collected, could be laid side to side to form a single wide mural (seen at the top of this post) and the final version had no ads, cost extra, and had a double gatefold cover that could be unfolded to show the full image, drawn by fan-favorite, young, up-and-coming artistic super star Jim Lee.

You can already guess the outcome. Retailers flooded the market with an estimated 8,186,500 copies of X-Men #1 to meet demand, and collectors snapped them up and preserved them. It’s everywhere in the collectors market. And today, you’ll be lucky to get a dollar for your copy of the best selling American single-issue comic book of all time — or at least, the best selling American single-issue comic book of all time that we have hard data on.