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COGNITIVE SERVICES
Insurance Brokerage
Leader: Marsh McLennan — 22.0% S1 · 48.0% CR3
S1
leader
CR3
top 3 combined
HHI
Unconcentrated
MARKET SIZE
US
How this is calculated
FORMULA
S1 = Marsh McLennan commission revenue / total commission revenue = 22.0%
CR3 = Marsh McLennan + Aon + Arthur J. Gallagher = 48.0%
HHI = Σ(share²) = 822 (Unconcentrated (HHI < 1,500))
DENOMINATOR
Commission Revenue — $95B (US)
US commercial insurance brokerage commission and fee revenue.
Size from: AM Best + Business Insurance rankings
TOP 3 PLAYERS
#1Marsh McLennan22.0%
#2Aon13.0%
#3Arthur J. Gallagher13.0%
METHODOLOGY NOTE
Marsh McLennan US brokerage commission revenue per AM Best and Business Insurance rankings divided by total US commercial brokerage market. Refreshed May 2026 — Arthur J. Gallagher overtook WTW for #3 globally and in the US after closing the $13.8B AssuredPartners acquisition in 2025; FY25 brokerage segment revenue was $12.2B (vs $9.9B 2024), and 20+ consecutive quarters of double-digit growth. WTW dropped to #4 per Business Insurance / MarshBerry. Validated against MMC, AON, AJG, and WTW 10-K segment disclosures.
Year: 2025
Geo: US
Firms: 35,000+
Historical S1 / CR3 trajectory
1990S1: 15%CR3: 32%Pre-consolidation era
2000S1: 18%CR3: 38%Marsh acquisitions
2010S1: 20%CR3: 42%Post-GFC consolidation
2020S1: 21%CR3: 44%Aon / WTW merger attempted
2025S1: 22%CR3: 45%Big 3 stable
Labor economics
REV / EMPLOYEE (leader)
$0.3M
industry avg $0.3M
SG&A % (leader)
19%
of revenue
Marsh McLennan FY2024 SG&A 19.0% (non-comp basis; comp $14.0B reported separately)
Related markets
Source Quality Hierarchy
Every market has a primary source plus 1–3 validation sources. Revenue numerators come from SEC 10-K filings; denominators validated against the Economic Census where available.
TIER 1Authoritative anchorsGovernment data + SEC filings
US Economic Census (data.census.gov) · SEC EDGAR / Company 10-Ks · BEA Industry Value-Added (FRED) · BLS QCEW · USGS Mineral Commodity Summaries · EIA Refinery Capacity Report · FDA device listings
TIER 2Leading commercial trackersIndustry-standard paid trackers
IDC Semiannual Software Tracker · Gartner Market Share & Magic Quadrant · IBISWorld NAICS reports · StatCounter Global Stats · eMarketer / Insider Intelligence · Synergy Research Group
TIER 3Category specialistsBest-in-class niche authorities
SIPRI (aerospace & defense) · IQVIA (pharma) · TrendForce (semiconductors) · CIMdata (CAD/PLM) · Nilson Report (payments) · Am Law 100 (legal) · ENR Top 500 (A&E) · AM Best (insurance) · SIA (staffing) · Ad Age (agencies) · Barron's / Cerulli (wealth) · Evaluate MedTech · Nielsen Gauge (streaming) · Gridwise (ride-hail) · Bloomberg Second Measure (delivery) · RC Top 100 (roofing) · SDM Top 100 (fire/safety) · Big 4 annual reports · ALM Intelligence (consulting)
Data vintage: Q2 2025 research compilation. Labels updated 2026-Q2. Tier 1 sources refreshed from FY2025 SEC filings where available. For full methodology see the Methodology page.