MOASS Meaning: Mother of All Short Squeezes

Start hereGameStop's short interest passed 100% of its float in January 2021. Yet the SEC staff concluded that positive sentiment, not buying to cover, sustained its rise. So was it a short squeeze at all?

01What 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. That makes it a prediction.

This page explains the term. It also sets out what the staff of the US Securities and Exchange Commission (SEC) found about the trading behind it. It does not say whether any stock will squeeze, and nothing here is investment advice.

02Understanding Short Squeezes

A short squeeze happens when a heavily shorted stock rises fast and short sellers rush to buy it back. Their buying can push the price higher still.

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. The shares then go back to the lender.

The risk is that a stock’s price can in principle keep rising. So, as the SEC staff report on 2021 notes, 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.

If the price jumps, the report explains, short sellers would face margin calls. They would have to post more collateral or exit their position. Those who exit have to buy the stock back. That buying pushes the price up further, which can force out other short sellers in turn.

A real example comes from Volkswagen. On 28 October 2008, Reuters reported that it had briefly become the world’s biggest company by market value. Short sellers betting on a fall were scrambling to find shares after a buying spree by Porsche.

03Where the phrase came from

The phrase is older than GameStop: it was in newspapers in the 1990s.

Barry Popik, who traces where words and phrases come from, found it in the Star Tribune of Minneapolis on 16 February 1994. There, a money manager predicted that “the mother of all short squeezes” would soon affect NordicTrack’s stock. Popik also found it in USA Today in 1995, about the bond market.

The 2008 Reuters report on Volkswagen quotes an analyst using the same phrase. Popik notes that the “mother of all” formula was used in the Gulf War of 1990–91, as the “Mother Of All Battles”.

By Popik’s record, the acronym MOASS appears in social-media posts from 2009 onward. It went viral in January 2021 with GameStop.

04What the SEC staff found about GameStop in 2021

In the SEC staff’s words: “While a short squeeze did not appear to be the main driver of events, and a gamma squeeze less likely, the episode highlights the role and potential impact of short selling and short covering.” Six authors later argued that the staff’s method may have missed a large volume of short sellers’ buying. The size of any squeeze is still an open question.

In October 2021 the SEC staff published the Staff Report on Equity and Options Market Structure Conditions in Early 2021. It is a staff report. Its own disclaimer says the Commission has expressed no view on its analysis, findings or conclusions.

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. The next day it reached an intraday high (its highest price during the day) of $483.00. By 19 February it had fallen as low as $40.59.

Short interest. This measures how many shares are currently sold short, as a percentage of the company’s shares. 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. The short-interest figures the SEC staff used are reported by the exchanges every two weeks, so a figure can be out of date.

Was it a short squeeze?

Partly, at moments. The staff found separate periods when GME rose sharply as known major short sellers covered their positions. During those times, the staff wrote, the covering likely helped push GME’s price up.

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 worn off.

The staff left open what drove the buyers: a desire to squeeze short sellers and profit from the rise, or belief in GameStop’s fundamentals. Either way, they concluded, “it was the positive sentiment, not the buying-to-cover, that sustained the weeks-long price appreciation of GameStop stock”.

Not everyone who studied the trading agrees. In February 2022, six authors (five at universities, one at SpotGamma) published a critique of the staff’s method. They wrote as the Ad Hoc Academic Committee on Equity and Options Market Structure Conditions in Early 2021.

The staff built their list of short sellers from trading records that begin on 24 December 2020. They then kept only the more heavily shorted half.

The critics argue that this start date means the method counts zero short positions on 23 December 2020. They also argue that keeping only the more heavily shorted half may leave out a large volume of covering purchases.

They extended the sample and added securities-lending data. With those, 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 (showing which accounts placed the trades) that the critics could not see. The critics 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”.

Short interest above 100%

A figure above 100% can look impossible. But short interest can pass 100% through ordinary share lending.

The same shares can be lent several times over, by one buyer after another, the report explains. 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

Fails to deliver are only a rough guide to naked short selling.

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, so the suspicion of naked shorting had something to go on.

But fails can come from ordinary (long) sales as well as short sales. That makes them an imperfect measure of naked short selling. And GME did not have persistent fails to deliver at the level of individual clearing members, the member firms of the clearing system.

Most clearing members cleared their fails within a few days.

Gamma squeeze

The staff “did not find evidence of a gamma squeeze in GME during January 2021”. The critics dispute how that was tested.

A call option gives its holder the right to buy a stock at a set price; a put option, the right to sell. A gamma squeeze happens when market makers who have written (sold) call options buy the stock to hedge them, pushing its price up.

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 critics argue that this test is too narrow. In their words, “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

The report ties the buying limits to the clearing system, which processes trades before they settle.

On 28 January 2021 several brokerages restricted trading in GME. On 27 January, the National Securities Clearing Corporation (NSCC) made intraday margin calls totalling $6.9 billion on 36 clearing members.

NSCC’s rules do not let it tell firms to stop trading particular stocks, the report notes. Some brokers chose to restrict trading in reaction to margin calls and capital charges imposed by NSCC.

The report also 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.

$347.51	Closing high on 27 January
$483.00	Intraday high the next day
122.97%	Short interest as a percent of float, January 2021
$6.9 billion	Intraday margin calls by NSCC on 36 clearing members, 27 January

From the SEC staff report of October 2021.

05What changed afterwards

One change since then matches a suggestion in the report: most broker-dealer trades now settle faster. Settlement is when the money and the shares change hands.

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. Despite the media attention to short squeezes, it said “the interplay between shorting and price dynamics is more complex than these narratives would suggest”.

On 15 February 2023 the SEC adopted rules to shorten the standard settlement cycle for most broker-dealer trades. The rules move it from two business days after the trade (T+2) to one (T+1). The compliance date was 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.

06Why It Resonates

MOASS names something easy to picture: short sellers forced to buy all at once, and the price running away. In our reading, GameStop’s January 2021 figures, set out above, made that picture feel close.

The record is harder to read, as the disagreement above shows. So the useful question about any squeeze claim is whose count it rests on, and what data they could see. A prediction from someone who owns the stock is not a finding from someone who studied the trades.

07Quick answers

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How we checked this · Last checked October 2026

• The GameStop figures and findings come from the SEC staff report of October 2021, read in the PDF. Quotations are the report's own words.
• The 2022 critique was read in the authors' summary on Columbia Law School's CLS Blue Sky Blog (22 February 2022).
• The phrase's history follows Barry Popik's dated record in The Big Apple and the 2008 Reuters report on Volkswagen.
• The SEC staff and the critique's authors disagree on how much of the rise was short covering. The page gives both views and does not settle it.
• The page describes the term and the record. It makes no prediction about any stock and gives no investment advice.

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