Inside the Portfolio

William Harrison's quarterly equity research letter. Concentrated value investing analysis, portfolio strategy, and long-term capital allocation insights — written for investors who think in years, not quarters.

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Equity Analysis

Deep-dive analysis of individual securities — business quality, competitive moat, valuation, and long-term return potential.

Portfolio Strategy

Capital allocation thinking, position sizing philosophy, and how William constructs a concentrated, conviction-driven portfolio.

Investment Framework

The mental models, valuation approaches, and long-term thinking that drive Sirmium Capital's investment process.

The Author

William Harrison

CHIEF INVESTMENT OFFICER · SIRMIUM CAPITAL

William Harrison applies a Buffett/Munger-influenced investment philosophy to long-term equity analysis. His quarterly research letter has become the intellectual backbone of Sirmium Capital's investment process.

Each issue focuses on a specific sector theme, individual security analysis, or portfolio strategy insight — written with the same rigor and transparency William applies to managing client portfolios.

"Good investing is mostly about doing very little, very well, with a long time horizon and the discipline not to ruin it."

— William Harrison

Latest Issue

Q2 2026 Research Letter

Q2 2026 Published by William Harrison

Investor Intelligence Report

In this quarter's letter, William explores how rising interest rates reshape competitive dynamics across sectors, which business models become more durable under financial pressure, and where patient investors are finding genuine long-term value in a market obsessed with short-term catalysts.

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About the Research Letter

William Harrison, Sirmium Capital's Chief Investment Officer and Portfolio Manager, writes every issue of Inside the Portfolio. It reflects his personal investment research and the thinking that drives Sirmium Capital's portfolio decisions.

Inside the Portfolio is published quarterly — four times per year. You will receive one issue per quarter, timed to coincide with William's portfolio review process.

No. Inside the Portfolio is an informational research letter for educational purposes only. It does not constitute investment advice, a solicitation, or an offer to buy or sell any security. Your individual circumstances require personalized advice. Please consult a qualified financial adviser.

Yes. The newsletter is free for all subscribers. Sirmium Capital provides it as a service to our clients and to the communities we serve. There is no charge, and you can unsubscribe at any time.