When it comes to accounting firms, the big are getting bigger. The top ten largest audit firms boosted their share of the external auditing market in 2019, according to a new report by research firm Audit Analytics.
The report finds that the market share held by the 10 biggest firms ticked up from 63.8 percent to 65.7 percent in 2019. Out of 5,985 publicly traded companies, 3,933 now use a top-10 audit firm. (The overall number of public companies grew only slightly, increasing .2 percent from 5,973 in 2018.)
The growth in the big firm market share can be mostly attributed to increased domination by the Big Four, as their percentage of the audit market rose to 49.2 percent in 2019 from 47.1 percent in 2018. The market share of the rest of the top ten firms actually dipped slightly, from 16.7 percent to 16.5 percent.
Ernst and Young led all firms with 15.5 percent of the total audit market (927 companies), followed by Deloitte with 12.5 percent of the market (748 companies).
The Big Four continues to have a tight grip on the market for big company clients, auditing almost 90 percent of large accelerated filers. In the categories of smaller reporting companies, however, non-Big Four top firms account for 23.1 percent of the market and the rest 73.9 percent are shared among 210 firms, highlighting the high competition in smaller company audit markets. 
Stephanie Liu is assistant editor at Internal Audit 360°