Here are some data I just put together on who audits U.S. listed Chinese companies. These data are by total fees collected in US$.
PwC and KPMG dominate mostly because they do most of the giant SOEs that are listed on NYSE. The biggest audit in China is China Mobile, which paid KPMG $14 million in 2010. This table does not include the many OTCBB and Pink Sheet companies, most of which were reverse mergers and use small accounting firms.
Here are the number of clients for each firm:
Deloitte has the largest number of clients, yet are third in total fees. That is mainly because Deloitte has none of the big SOEs.
The Big Four have 88% of the market. The Herfindahl Hirschmann Index is 2149. Anything over 1800 is generally considered highly concentrated.
The data come from Audit Analytics. I combined three BDO firms and three Crowe Horwath firms in the table.