Breaking down the stocks Guy Spier (Aquamarine) bought, sold, and held in Q3 2025, including their holdings at the end of the quarter. All data sourced from Aquamarine's 13F filed on October 20, 2025.
Who are Guy Spier and Aquamarine Capital?
Guy Spier is the founder and portfolio manager of Aquamarine Fund (commonly referred to as Aquamarine Capital). The fund is known for its highly concentrated portfolio, typically consisting of 10-15 stocks, with the top 7 holdings comprising approximately 75% of assets, and cash holdings averaging around 5-6% when attractive opportunities are limited. His investment strategy is a global value investing approach inspired by Warren Buffett's original 1950s partnerships, emphasizing long-term compounding of intrinsic value and capital preservation while avoiding leverage and excessive trading. Spier focuses on undervalued, high-quality companies that occupy the "economic high ground," with strong qualitative factors like economic moats, high returns on invested capital, share repurchase programs, resilient brands, ecosystem control, and the ability to endure and compound sustainably over decades, often in sectors like financial services, luxury goods, and emerging market infrastructure.
Guyspier.com
Aquamarinefund.com
Guy Spier on X
Q3 '25 13F filed with SEC
Holdings in Q3 2025
| Ticker | Company | Weight | Change | Value |
|---|---|---|---|---|
| BRK-B | Berkshire Hathaway | 22.3% | $70.69M | |
| AXP | American Express | 22.0% | $69.75M | |
| BAC | Bank of America | 12.5% | $39.61M | |
| MA | Mastercard | 11.8% | $37.4M | |
| RACE | Ferrari | 9.1% | $28.98M | |
| BRK-A | Berkshire Hathaway | 7.1% | $22.63M | |
| MU | Micron | 4.2% | Trimmed (-60%) | $13.39M |
| MCO | Moody's | 4.1% | $12.87M | |
| BABA | Alibaba | 2.7% | $8.49M | |
| DJCO | Daily Journal | 1.7% | $5.35M | |
| GOOGL | Alphabet | 1.2% | $3.89M | |
| SRG | Seritage Growth Properties | 0.7% | $2.12M | |
| AMR | Alpha Metallurgical | 0.4% | $1.31M | |
| CNR | Core Natural Resources | 0.3% | Added (+33%) | $897K |
Current Investment Strategy
Guy Spier's Aquamarine Fund maintained its signature ultra-concentrated approach in Q3 2025, with 77% of the $317 million portfolio allocated across just five holdings—Berkshire Hathaway, American Express, Bank of America, Mastercard, and Ferrari—reflecting his Buffett-inspired focus on businesses with durable moats and long-term compounding potential. The quarter's only notable move was a 60% reduction in Micron Technology, underscoring Spier's disciplined patience and preference for financial services, payment networks, and luxury franchises over semiconductor volatility.
New Investments
Aquamarine did not open any new positions during Q3 2025.
Added, Trimmed, and Exited
Added
Aquamarine Capital increased its position in Core Natural Resources (CNR) by 2,640 shares, bringing the total from 8,100 to 10,740 shares—a 32.6% increase in the position size.
What it means: This addition to an already profitable position (up 19.76% in the quarter) suggests Guy Spier sees continued value in the natural resources sector despite it remaining a relatively small holding. The decision to add after positive performance indicates conviction that the opportunity hasn't fully played out, possibly reflecting views on commodity cycles or the company's specific competitive positioning within the resource space.
Trimmed
Aquamarine Capital significantly reduced its stake in Micron (MU) by 120,000 shares—a dramatic 60% reduction from 200,000 to just 80,000 shares.
What it means: This substantial trim follows a steep -45.70% decline in the position's value, suggesting Spier is either cutting losses to redeploy capital into more attractive opportunities or reducing exposure to what has become an underperforming investment. The move away from this cyclical semiconductor position aligns with Aquamarine's stated preference for companies with sustainable competitive advantages and "economic high ground"—characteristics that may be less evident in the volatile memory chip sector. This disciplined reduction demonstrates willingness to correct course when a position doesn't perform as expected.
Exited
Aquamarine Capital did not fully liquidate any positions during Q3 2025.
Disclaimer: All posts are for informational purposes only. They are NOT a recommendation to buy or sell the securities discussed. Please do your own research and due diligence before investing your money.
