Greenshoe Option
A greenshoe option, formally known as an overallotment option, is a provision in an underwriting agreement that gives underwriters the right to sell additional shares — typically up to 15% more than the original offering size — to stabilize the stock price after an IPO.
The greenshoe option takes its name from the Green Shoe Manufacturing Company, which was the first company to grant such a provision to its underwriters in 1960. Formally called an overallotment option, the greenshoe is now a standard feature of virtually every large U.S. IPO and is permitted under SEC Rule 10b-4 and Regulation M.
The mechanics of the greenshoe involve the underwriter selling more shares than the company is issuing. In a typical structure, if a company is selling 10 million shares, the underwriter may actually sell 11.5 million shares to investors — the extra 1.5 million being the 15% overallotment. The underwriter is effectively short 1.5 million shares at the outset. It covers this short position in one of two ways: either by exercising the greenshoe option to purchase additional newly issued shares from the company at the offering price, or by buying shares in the open market.
This structure creates a price stabilization mechanism. If the stock trades below the offering price in the days following the IPO — suggesting weak demand — the underwriter purchases shares in the open market, which supports the price and simultaneously covers the short position. If the stock trades well above the offering price, the underwriter exercises the greenshoe option and purchases the additional shares from the company at the offering price, allowing the company to raise up to 15% more capital.
For the issuing company, the greenshoe option means that if the IPO is successful, the company receives additional proceeds from the exercise of the option. For investors, the greenshoe acts as a de facto price support mechanism in the immediate aftermarket, which can reduce the volatility of a newly listed stock.
The SEC requires underwriters to disclose greenshoe arrangements in the prospectus. The existence of a greenshoe is publicly known before trading begins, and its exercise or non-exercise must be reported. Investors should note that once the greenshoe is fully exercised or the stabilization period expires, underwriter price support ends and the stock trades on its own fundamentals and market demand.