THE ARTICLE · 8 MIN
What MOASS means
MOASS stands for “Mother Of All Short Squeezes”. People use it for a short squeeze bigger than any that has happened before. Since January 2021 it has been used above all about GameStop.
The older phrase has been used after the fact, for squeezes that happened (see below). In the GameStop era, MOASS names a squeeze people expect, not one that has happened: a prediction. This page explains the term and what the US Securities and Exchange Commission’s staff found about the trading it grew out of. It does not say whether any stock will squeeze, and nothing here is investment advice.
Understanding Short Squeezes
Short selling is selling a stock you do not own. The usual way is to borrow shares, sell them, and hope to buy them back later at a lower price to return to the lender. The SEC staff report on 2021 points out why this is risky: a stock’s price can in principle keep rising, so a short seller “can lose more than the value of their original investment”. Brokers usually require collateral in a margin account of at least 50% of the shorted position, on top of the cash from the sale.
A short squeeze is what can happen when a heavily shorted stock rises fast. In the report’s words, if the price jumps, short sellers “would face margin calls requiring them either to post additional collateral or to exit their position”. Those who exit have to buy the stock back, and that buying pushes the price up further, which can force out other short sellers in turn.
A real example: on 28 October 2008, Reuters reported that Volkswagen had briefly become the world’s biggest company by market value, as short sellers betting on a fall scrambled to find shares “after a buying spree by Porsche”.
Where the phrase came from
The phrase is older than GameStop. The etymologist Barry Popik found “the mother of all short squeezes” in the Star Tribune of Minneapolis on 16 February 1994, in a money manager’s prediction about NordicTrack’s stock, and in USA Today in 1995 about the bond market. The Reuters report on Volkswagen in 2008 quotes an analyst calling it “the mother of all short squeezes”. Popik traces the “mother of all” formula to the Gulf War of 1990–91.
The acronym MOASS appears in social-media posts from 2009 onward, by Popik’s record, and it went viral in January 2021 with GameStop.
What the SEC staff found about GameStop in 2021
In October 2021 the SEC staff published the Staff Report on Equity and Options Market Structure Conditions in Early 2021. It is the SEC staff’s account of the episode, and it is a staff report: its own disclaimer says the Commission “has expressed no view regarding the analysis, findings, or conclusions contained herein”.
The price. GameStop (GME) had ended 2020 at a little under $20 a share. By 27 January 2021 it closed at $347.51, more than 1,600% above its close on 11 January, and the next day it reached an intraday high of $483.00. By 19 February it had fallen as low as $40.59.
Short interest. GameStop’s short interest hovered around 100% of shares outstanding from 2019 to early 2021, peaking at 109.26% on 31 December 2020. Measured against the public float, it reached 122.97% in January 2021. The two numbers differ because they divide by different things: all shares outstanding, or only the shares available to trade.
Was it a short squeeze?
Partly, at moments. The staff found discrete periods when GME rose sharply as known major short sellers covered their positions, and that “during these times, short sellers covering their positions likely contributed to increases in GME’s price.”
But the report’s overall finding runs the other way. Buying by traders with large short positions was “a small fraction of overall buy volume”, and the price stayed high “after the direct effects of covering short positions would have waned”. Its conclusion:
“Whether driven by a desire to squeeze short sellers and thus to profit from the resultant rise in price, or by belief in the fundamentals of GameStop, it was the positive sentiment, not the buying-to-cover, that sustained the weeks-long price appreciation of GameStop stock.”
Elsewhere the staff put it more briefly: “a short squeeze did not appear to be the main driver of events”.
Not everyone who studied the trading agrees. In February 2022 six academics writing as the Ad Hoc Academic Committee on Equity and Options Market Structure Conditions in Early 2021 (Joshua Mitts, Robert Battalio, Jonathan Brogaard, Matthew Cain, Lawrence Glosten and Brent Kochuba) published a critique of the staff’s method. The staff built their list of short sellers from trading records that begin on 24 December 2020 and kept only the more heavily shorted half; the academics argue that this start date means the method counts “zero short positions on December 23, 2020”, and that keeping only the more heavily shorted half may leave out a large volume of covering purchases. Extending the sample and adding securities-lending data, they report “evidence that a nontrivial fraction of the trading volume in GameStop’s stock consisted of purchases by short sellers covering their positions”.
Where that leaves it: open. Both sides agree that short covering pushed the price up at some moments. They disagree on how much of the whole rise it explains. The staff had non-public, deanonymised data the academics could not see; the academics used a longer window and lending records the staff left out, and they say themselves that without the staff’s data they “are unable to pin down the magnitude of a short squeeze or gamma squeeze”. Neither account settles the size of the squeeze.
Short interest above 100%
Short interest can pass 100% through ordinary share lending. The report explains that the same shares can be “lent multiple times by successive purchasers”: if someone buys a share from a short seller and lends it out again, it counts as sold short twice. GME was the only stock the staff saw with short interest above its shares outstanding in January 2021.
Naked short selling and fails to deliver
A “naked” short sale is one made without arranging to borrow the shares, so the seller fails to deliver them on time. The staff did see spikes in GME’s fails to deliver. But fails can come from ordinary (long) sales as well as short sales, which makes them “an imperfect measure of naked short selling”, and GME “did not experience persistent fails to deliver at the individual clearing member level”. Most clearing members cleared their fails within a few days.
Gamma squeeze
A gamma squeeze happens when market makers who have written call options buy the stock to hedge them, pushing its price up. The staff “did not find evidence of a gamma squeeze in GME during January 2021”. The jump in options trading by individual customers was mostly in put options, not calls, and market makers were buying call options rather than writing them. The academic critique above argues that this test is too narrow: “what matters is not the type of option at issue – put or call – but rather the direction of the hedging”, so market makers hedging put options can also end up buying the stock.
Why brokers restricted buying
On 28 January 2021 several brokerages restricted trading in GME. The report ties this to the clearing system. On 27 January, the National Securities Clearing Corporation (NSCC) made intraday margin calls totalling $6.9 billion on 36 clearing members. The report notes that NSCC’s rules do not let it tell firms to stop trading particular stocks; some brokers chose to restrict trading “in reaction to margin calls and capital charges imposed by NSCC”. It records that witnesses at a Congressional hearing testified that the restrictions did not come from pressure by hedge funds.
Not just GameStop. AMC, another stock caught up in the January 2021 trading restrictions, had short interest of 11.4% of its float in January 2021, against GME’s 122.97%. And on 27 January, four other stocks, AMC among them, had bigger one-day price rises than any single-day rise in GME.
What changed afterwards
The report’s conclusions named four areas for further consideration. Under the first, why brokers restricted trading, it suggested shortening the settlement cycle; under the fourth, short selling, it called for better reporting of short sales and said “the interplay between shorting and price dynamics is more complex than these narratives would suggest.” On 15 February 2023 the SEC adopted rules shortening the standard settlement cycle for most broker-dealer trades from two business days after the trade (T+2) to one (T+1), with a compliance date of 28 May 2024. SEC Chair Gary Gensler said the change addressed one of the four areas the staff recommended “in response to the meme stock events of 2021”.
How to read a squeeze claim
The 2021 record gives a few questions worth asking of any post that says a squeeze is coming:
- Short interest of what, and on what date? Percent of float and percent of shares outstanding are different numbers, and the short-interest figures the SEC staff used are reported by the exchanges every two weeks, so a figure can be out of date.
- Does above 100% prove something illegal? Not by itself: the SEC staff showed how the same shares, lent again, are counted twice.
- Who was buying? In January 2021, covering by short sellers was “a small fraction of overall buy volume” by the SEC staff’s count; the academics found “a nontrivial fraction” of trading volume and argued the staff’s method may have missed a large volume of it. When two studies of the same trades disagree, the size is not settled.
- Is a fail to deliver the same as a naked short? No: the staff called fails an imperfect measure, since they also come from ordinary sales.
- Who is making the claim, and what do they hold? A prediction from someone who owns the stock is not a finding from someone who studied the trades.
This page describes what happened and what the regulator’s staff found. It does not recommend buying, selling or holding anything.
Sources
- U.S. Securities and Exchange Commission staff, Staff Report on Equity and Options Market Structure Conditions in Early 2021 (14 October 2021), sections 1, 3.2, 3.4–3.6 and 4: https://www.sec.gov/files/staff-report-equity-options-market-struction-conditions-early-2021.pdf
- U.S. Securities and Exchange Commission, “SEC Finalizes Rules to Reduce Risks in Clearance and Settlement”, press release 2023-29 (15 February 2023): https://www.sec.gov/newsroom/press-releases/2023-29
- Sarah Marsh, “Short sellers make VW the world’s priciest firm”, Reuters (28 October 2008), archived copy: https://web.archive.org/web/20210123004118/https://www.reuters.com/article/us-volkswagen/short-sellers-make-vw-the-worlds-priciest-firm-idUSTRE49R3I920081028
- Joshua Mitts, Robert H. Battalio, Jonathan Brogaard, Matthew D. Cain, Lawrence R. Glosten and Brent Kochuba, “An Academic Critique of the SEC’s GameStop Report”, CLS Blue Sky Blog, Columbia Law School (22 February 2022): https://clsbluesky.law.columbia.edu/2022/02/22/an-academic-critique-of-the-secs-gamestop-report/
- Barry Popik, “Mother Of All Short Squeezes (MOASS)”, The Big Apple (31 January 2021): https://www.barrypopik.com/new_york_city/entry/mother_of_all_short_squeezes/
Checked September 2026.
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