Arthur J. Gallagher & Co.
MX ˙ BMV ˙ US3635761097
SecurityMX:AJG / Arthur J. Gallagher & Co.
InstitutionMarshall Wace, Llp
Latest Disclosed Ownership276,420 shares
Latest Disclosed Value $ 59,867,045
Marshall Wace, Llp reports 227.79% increase in ownership of AJG / Arthur J. Gallagher & Co.

On May 14, 2026 - Marshall Wace, Llp filed a 13F-HR form disclosing ownership of 276,420 shares of Arthur J. Gallagher & Co. (MX:AJG) valued at $59,867,045 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 13, 2026 disclosing 84,329 shares of Arthur J. Gallagher & Co.. This represents a change in shares of 227.79% during the quarter.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date		 Effective
Date		Form Security Class ID Avg Price
Paid (Est)		 Reported
Shares		 ΔShares ΔShares
(%)		 Reported
Value
(x1000)		 ΔValue
(%)		 Alloc
(%)		 ΔAlloc ΔAlloc (%) Cost Basis
(x1000)		 Unrealized
Gain/Loss
(x1000)
2026-05-14 2026-03-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 276,420 192,091 227.79 59,867 174.33 0.0282
2026-02-13 2025-12-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 84,329 -15,268 -15.33 21,824 -29.26 0.0199
2025-11-13 2025-09-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 99,597 -47,541 -32.31 30,849 -34.50 0.0313
2025-08-13 2025-06-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 147,138 -97,559 -39.87 47,102 -44.25 0.0531
2025-05-15 2025-03-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 244,697 -61,223 -20.01 84,479 -2.71 0.1073
2025-02-13 2024-12-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 305,920 290,098 1,833.51 86,835 1,850.91 0.1044
2024-11-14 2024-09-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 15,822 -23,528 -59.79 4,452 -56.38 0.0054
2024-08-14 2024-06-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 39,350 -6,429 -14.04 10,204 -10.86 0.0136
2024-05-15 2024-03-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 45,779 38,335 514.98 11,447 583.75 0.0174
2024-02-14 2023-12-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 7,444 7,444 1,674 0.0028
2023-11-14 2023-09-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -50,417 -100.00 0 -100.00
2023-08-14 2023-06-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 50,417 48,702 2,839.77 11,070 3,275.00 0.0216
2023-05-15 2023-03-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 1,715 1,715 328 0.0007
2022-11-14 2022-09-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -29,300 -100.00 0 -100.00
2022-08-15 2022-06-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 29,300 29,300 4,777 0.0098
2022-05-16 2022-03-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -101,673 -100.00 0 -100.00
2022-02-14 2021-12-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 101,673 101,673 17,251 0.0319
2021-11-15 2021-09-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -105,330 -100.00 0 -100.00
2021-08-13 2021-06-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 105,330 105,330 14,755 0.0719
2021-02-16 2020-12-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -5,100 -100.00 0 -100.00
2020-11-16 2020-09-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 5,100 5,100 538 0.0034
2020-08-13 2020-06-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -16,994 -100.00 0 -100.00
2020-05-15 2020-03-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 16,994 14,627 617.96 1,385 515.56 0.0138
2020-02-14 2019-12-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 2,367 2,367 -86.07 225 -83.75 0.0015
2018-11-14 2018-09-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -5,141 -100.00 0 -100.00
2018-08-14 2018-06-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 5,141 -226,959 -97.79 336 -97.89 0.0050
2018-05-15 2018-03-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 232,100 232,100 4,414.69 15,952 4,647.62 0.6612
2017-05-12 2017-03-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -47,092 -100.00 0 -100.00
2017-02-10 2016-12-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 47,092 47,092 2,447 0.0161
2015-02-17 2014-12-31 13F ARTHUR J GALLAGH COMMON STOCK 363576109 0 -19,594 -100.00 0 -100.00
2014-11-13 2014-09-30 13F ARTHUR J GALLAGH COMMON STOCK 363576109 19,594 19,594 888 0.0128
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.