4 institutions reported holding $58.7M of MPLX LP (MPLXP) in SEC 13F filings for 2026-03-31. Largest institutional holders: GROUP ONE TRADING LLC ($28.6M), IMC-Chicago, LLC ($16.1M), SIMPLEX TRADING, LLC ($14.0M), SUMMIT SECURITIES GROUP LLC ($0). Source: SEC Form 13F.
| Rank | Institution | Value | Shares | Change |
|---|---|---|---|---|
| 1 | GROUP ONE TRADING LLC | $28.6M | 501,400 | Added |
| 2 | IMC-Chicago, LLC | $16.1M | 282,300 | Added |
| 3 | SIMPLEX TRADING, LLC | $14.0M | 245,200 | Trimmed |
| 4 | SUMMIT SECURITIES GROUP LLC | $0 | 0 | Exited |
Source: SEC Form 13F filings · as of 2026-03-31