SOUTHEASTERN ASSET MANAGEMENT INC/TN/ reported AVANTOR INC (AVTR) in 3 quarterly 13F filings from 2025 Q3 through 2026 Q1. Peak portfolio weight reached 3.28% in 2025 Q3. The latest visible filing shows AVTR at 1.36% of the fund.
This page tracks quarterly shares, estimated market value, portfolio weight, filing dates, and disclosure-aligned stock prices directly from SEC EDGAR 13F filings.
This page is designed to answer the real investor question behind a 13F filing: how meaningful was SOUTHEASTERN ASSET MANAGEMENT INC/TN/'s position in AVANTOR INC, and how did that conviction change over time? You can read the holding window, peak weight, latest reported size, disclosure timing, and quarter-by-quarter changes without piecing the story together from raw SEC rows.
AVTR was reported at 1.36% of portfolio in the most recent visible filing.
Peak weight helps separate a token disclosure from a real conviction holding the fund genuinely cared about.
Longer holding windows often tell a very different story from short-lived tactical trades or one-quarter experiments.
Knowing that a fund owned a stock is useful. Knowing whether it was a 0.20% placeholder or a true high-conviction position is where the signal actually starts.
As of 2026 Q1 — sorted by position size
These are the practical questions this page is built to answer before you even open the full history table.
SOUTHEASTERN ASSET MANAGEMENT INC/TN/ reported AVTR across 3 quarterly 13F filings, from 2025 Q3 through 2026 Q1.
The largest reported portfolio weight for AVTR was 3.28% in 2025 Q3.
The most recent filing on this page is 2026 Q1, when SOUTHEASTERN ASSET MANAGEMENT INC/TN/ reported 3,520,212 shares, equal to 1.36% of portfolio, with an estimated market value of $27.6M.
The chart compares SOUTHEASTERN ASSET MANAGEMENT INC/TN/'s quarterly AVTR portfolio weight with the stock's indexed share price, so you can see whether the fund was building, trimming, or holding the position as price moved.