MASON CAPITAL MANAGEMENT LLC — 13F Holdings & Portfolio
CIK 1218735 · latest 13F-HR filed 2026-05-15
AUM is the long-equity portion reported on Form 13F-HR. Excludes short positions, cash, foreign holdings, and non-13F assets. For informational purposes only — not investment advice.
$612.9M
Long-equity book
7
Distinct positions
2026-03-31
Filed 2026-05-15
+2 / −4 / ↑2 / ↓3
vs 2025-12-31
| Name | Title / Status | Ownership | Type |
|---|
Top Adds (vs prior quarter)
- ATS CORPORATION$34.0M +7.9%
- CLEAR CHANNEL OUTDOOR HLDGS$1.6M +7.2%
Top Trims
- BROOKDALE SENIOR LIVING INC-$8.1M -21.0%
- READY CAPITAL CORP-$1.2M -15.0%
- SIGNATURE BANK-$144.0K -35.6%
Exited Positions
- SOLSTICE ADV MATERIALS INC$30.8M
- JBS N.V.$18.8M
- BORR DRILLING LTD$8.8M
- MESA LABORATORIES INC$5.5M
Rows tagged Call or Put are options positions, not stock. Per SEC Form 13F-HR, Value shows the notional value of the underlying (shares covered × underlying price), not the option premium. Shares is the number of underlying shares covered (divide by 100 for contract count).
| # | Issuer | Symbol | CUSIP | Value | Weight | Shares | Type |
|---|---|---|---|---|---|---|---|
| 1 | ATS CORPORATION | ATS | 00217Y104 | $462.6M | 75.48% | 16,404,170 | SH |
| 2 | ENVIRI CORP | NVRI | 415864107 | $88.2M | 14.39% | 4,494,536 | SH |
| 3 | BROOKDALE SENIOR LIVING INC | BKD | 112463104 | $30.6M | 4.99% | 2,233,741 | SH |
| 4 | CLEAR CHANNEL OUTDOOR HLDGS | CCO | 18453H106 | $23.3M | 3.80% | 9,828,401 | SH |
| 5 | READY CAPITAL CORP | RC | 75574U101 | $7.0M | 1.14% | 4,319,933 | SH |
| 6 | JELD-WEN HOLDING INC | JELD | 47580P103 | $963.3K | 0.16% | 776,885 | SH |
| 7 | SIGNATURE BANK | SBNY | 82669G104 | $260.0K | 0.04% | 400,000 | SH |
| Period | Filed | AUM | Holdings | Accession |
|---|---|---|---|---|
| 2026-03-31 | 2026-05-15 | $612.9M | 7 | 0001104659-26-062410 |
| 2025-12-31 | 2026-02-17 | $561.6M | 9 | 0001104659-26-016335 |
| 2025-09-30 | 2025-11-14 | $491.4M | 6 | 0001104659-25-111862 |