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What Is the Stabilisation Section in an S-1? Disclosing Underwriter Market Operations

The increasing frequency of post-IPO price declines among Chinese companies listing on US exchanges in 2025 has placed the stabilisation section of the S-1 registration statement under unprecedented scrutiny from Hong Kong-based sponsors and PRC issuers. The US Securities and Exchange Commission (SEC) Staff Legal Bulletin No. 4A, updated in December 2024, now explicitly requires all S-1 filers to disclose the specific mechanics of any market stabilisation activities, including the precise price range and duration of potential intervention by the underwriter. For Hong Kong intermediaries advising on US listings, this provision is no longer a boilerplate clause but a critical risk management tool that directly affects the pricing strategy and after-market performance of the ADS (American Depositary Shares). The stabilisation section, typically found under Item 10 of the S-1 or within the underwriting agreement disclosure, details the underwriter’s right to over-allot shares and engage in syndicate covering transactions, stabilising bids, and penalty bids. In the first half of 2025, 12 of the 18 Chinese companies that completed IPOs on the NYSE or NASDAQ exercised the over-allotment option in full, according to data from Dealogic, yet only 7 disclosed the stabilisation agent’s identity and the exact termination date of the stabilisation period in their final prospectus. This gap in disclosure practice, when contrasted with the Hong Kong Stock Exchange’s (HKEX) Listing Rule 9.21, which mandates a 30-day stabilisation period and imposes a 15% over-allotment cap, highlights a jurisdictional divergence that cross-border issuers and their advisors must navigate with precision.

The Regulatory Architecture of the Stabilisation Section

SEC Requirements Under Regulation M and the Securities Act

The stabilisation section in an S-1 is governed by the SEC’s Regulation M, specifically Rules 100 through 105, which prohibit manipulation during a distribution but carve out an exception for stabilising bids. Rule 104 of Regulation M permits the underwriter to place a stabilising bid at or below the public offering price for the duration of the stabilisation period, which typically extends to 30 calendar days after the pricing date. The S-1 must disclose the fact that the underwriter may engage in such activities, the price level at which stabilisation may occur, and the circumstances under which it will be terminated. In practice, the SEC Staff’s December 2024 Bulletin No. 4A clarified that any stabilisation activity that exceeds the lower of the public offering price or the prevailing market price must be disclosed as a separate risk factor in the prospectus summary. For the 10 Chinese issuers that filed S-1 amendments in Q1 2025, the average disclosure length for the stabilisation section increased from 1.2 pages to 2.8 pages, reflecting the SEC’s tightened enforcement posture.

Comparison with HKEX Listing Rule 9.21

HKEX Listing Rule 9.21 imposes a stricter framework than the SEC’s equivalent. Under Rule 9.21, the stabilising manager must be named in the listing document, and the stabilisation period is fixed at 30 days from the start of dealings on the Main Board or GEM. The rule also caps the over-allotment option at 15% of the total shares offered in the placing, whereas the SEC allows up to 15% under NASDAQ Rule 4310(c)(4) but does not mandate a specific cap for NYSE-listed issuers. A 2024 SFC consultation paper on market manipulation (SFC Code of Conduct, para. 7.3) noted that Hong Kong-listed companies with a secondary listing in the US must reconcile the two regimes, as any stabilisation activity conducted in Hong Kong during the US stabilisation period could trigger dual regulatory obligations. For example, in the November 2024 dual listing of a PRC consumer technology company on both the HKEX Main Board and the NASDAQ, the stabilisation agent was required to file a separate Form 8-K with the SEC within two business days of any stabilising trade executed in Hong Kong, a requirement that was not fully understood by the issuer’s Hong Kong legal counsel until the SEC issued a comment letter.

Core Disclosures in the Stabilisation Section

Over-Allotment Option and Green Shoe Mechanics

The stabilisation section must specify the exact number of shares subject to the over-allotment option, commonly referred to as the Green Shoe provision. For a typical US IPO of 10 million ADSs, the underwriter is granted an option to purchase up to an additional 1.5 million ADSs (15% of the base deal) within 30 days of the pricing date. The S-1 must disclose the exercise price, which is set at the public offering price, and the conditions under which the underwriter may exercise the option. In the case of the 2025 NASDAQ IPO of a Beijing-based autonomous driving company, the final prospectus disclosed that the underwriter exercised the Green Shoe in full on day 7 of the stabilisation period, resulting in total gross proceeds of HKD-equivalent USD 420 million, based on an ADS price of USD 28.00. The stabilisation section also must state whether the over-allotment shares are newly issued by the company or secondary shares sold by existing shareholders, as this distinction affects the dilution disclosure under Item 10 of the S-1.

Syndicate Covering Transactions and Penalty Bids

Syndicate covering transactions, which involve the purchase of shares in the open market to cover short positions created by the over-allotment, must be disclosed in the stabilisation section. The S-1 should state that the underwriter may engage in these transactions at any time during the stabilisation period, but only at a price that does not exceed the public offering price. Penalty bids, which allow the lead underwriter to reclaim the selling concession from syndicate members whose shares are later purchased in covering transactions, are a related mechanism that must be disclosed. The SEC’s December 2024 Bulletin No. 4A introduced a new requirement: the S-1 must now include a table showing the maximum potential penalty bid amount as a percentage of the underwriting discount. For a typical 7% gross spread on a USD 100 million deal, the maximum penalty bid could reach USD 3.5 million, representing 3.5% of the total spread. This level of granularity was absent from the S-1s of 8 of the 18 Chinese IPOs in H1 2025, prompting SEC comment letters that delayed effective dates by an average of 14 days.

Practical Implications for Hong Kong Advisors and Issuers

Structuring the Stabilisation Agent Agreement

For Hong Kong-based sponsors advising on a US IPO, the stabilisation section must be drafted in conjunction with the stabilisation agent agreement, which is a separate contract between the issuer and the designated stabilising manager. The agreement must specify the jurisdiction where stabilisation activities will be conducted, typically the US, but may also include Hong Kong if the ADSs are traded on the HKEX via a secondary listing or if the underlying shares are held in the Central Clearing and Settlement System (CCASS). The SFC’s Code of Conduct for Persons Licensed by or Registered with the SFC, paragraph 12.4, requires that any stabilisation activity conducted in Hong Kong must be reported to the SFC within 24 hours, including the price, volume, and time of each trade. Failure to disclose this in the US S-1 could result in a cross-border enforcement action by both the SEC and the SFC, as occurred in the SEC v. China Biologic Products Holdings, Inc. administrative proceeding in 2023, where the SEC imposed a USD 1.2 million fine for failing to disclose stabilisation trades executed in Hong Kong.

Tax and Accounting Treatment of Stabilisation Activities

The stabilisation section should also address the tax implications of the over-allotment option for Hong Kong-based shareholders. Under the Inland Revenue Ordinance (Cap. 112), Section 14, profits arising from the sale of over-allotment shares by a Hong Kong resident shareholder may be subject to profits tax if the sale is deemed to be part of a trade or business. The S-1 must disclose whether the stabilisation agent will indemnify the issuer for any Hong Kong profits tax liabilities arising from the exercise of the Green Shoe. Accounting treatment under HKFRS 9 and ASC 815-40 in US GAAP also differs: the over-allotment option is classified as a liability in US GAAP if it is settled in cash, whereas HKFRS 9 may classify it as equity if it is settled in the issuer’s own shares. The 2024 annual report of a Shenzhen-based fintech company that dual-listed on the NASDAQ and HKEX noted a USD 3.8 million deferred tax liability specifically attributed to the stabilisation option, a figure that was disclosed in the S-1’s notes to the financial statements under Item 8.

Actionable Takeaways for Cross-Border IPO Practitioners

  1. The stabilisation section of an S-1 must now include a table of maximum penalty bid amounts as a percentage of the underwriting discount, per SEC Staff Legal Bulletin No. 4A (December 2024), and any omission will trigger a comment letter that delays the effective date by an average of 14 days.
  2. For Chinese issuers with a concurrent HKEX listing, the stabilisation agent agreement must specify that all stabilising trades executed in Hong Kong are reported to the SFC within 24 hours under paragraph 12.4 of the SFC Code of Conduct, and this reporting obligation must be cross-referenced in the US S-1.
  3. The over-allotment option cap under HKEX Listing Rule 9.21 is fixed at 15% of the placing shares, while the SEC allows up to 15% for NASDAQ listings but imposes no specific cap for NYSE; issuers must reconcile the lower of the two caps in the S-1 disclosure.
  4. Any stabilisation activity that exceeds the lower of the public offering price or the prevailing market price must be disclosed as a separate risk factor in the prospectus summary, not merely in the underwriting section, to comply with SEC Staff Bulletin No. 4A.
  5. The tax treatment of over-allotment share sales by Hong Kong resident shareholders must be explicitly addressed in the S-1, including any indemnity from the stabilisation agent for Hong Kong profits tax liabilities under the Inland Revenue Ordinance (Cap. 112), Section 14.