First published: 7 October 2026
Big4News’ Who Audits? project tracks the audit firms responsible for auditing major companies around the world.
The project is designed to answer a simple question that is surprisingly difficult to answer systematically: who audits the world’s largest and most important companies?
Big4News compiles datasets covering major stock-market indices as well as other groups of companies, such as the largest companies in particular industries or sectors.
For each dataset, Big4News identifies the current external auditor of every company and, where the information is publicly available, records how long the firm has held the mandate and the latest disclosed audit fee.
The resulting datasets allow readers to examine audit-market concentration, individual firm market share, auditor tenure and the distribution of major-company audits between Deloitte, EY, KPMG, PwC and other firms.
This page explains how the data is collected, interpreted and checked.
What we record
The core Who Audits? datasets generally contain four fields:
Company — the company included in the relevant dataset.
Auditor — the audit firm responsible for the company’s external statutory audit.
Since — the first financial year audited by the current audit firm, where this can be established with sufficient confidence.
Audit fee — the latest publicly disclosed fee attributable to the external audit, normally taken from the company’s most recent annual report or equivalent filing.
Some markets or datasets require additional fields. For example, companies subject to joint-audit requirements may have two auditors and therefore two corresponding tenure dates.
Primary sources
Big4News relies wherever possible on primary corporate and regulatory sources.
These include:
annual reports and audited financial statements;
proxy statements and shareholder-meeting documents;
statutory auditor reports;
regulatory filings;
stock-exchange disclosures;
auditor appointment and reappointment announcements;
company investor-relations materials; and
historical annual reports where required to establish auditor tenure.
Secondary sources may be used to help locate or corroborate information, but material data points are normally verified against primary documentation wherever practical.
Identifying the auditor
The auditor shown in the dataset is the firm signing the statutory external audit opinion for the relevant financial year.
Where an audit is performed through a local member firm of an international network, Big4News normally classifies the auditor under the corresponding global network — for example, PwC, Deloitte, EY or KPMG — while preserving distinctions where they are relevant to understanding the engagement.
The legal entity signing an audit opinion may differ from the name commonly used for the international network.
Where two audit firms jointly sign the statutory audit, both are recorded.
What “Since” means
The Since column refers to the first financial year audited by the current auditor.
It is intended to measure the duration of the audit relationship rather than simply the date on which shareholders most recently voted to appoint or reappoint the auditor.
Auditor appointments are commonly renewed annually even where the underlying audit relationship has existed for decades.
How the start year is established
Where possible, Big4News identifies the first year directly from historical annual reports, appointment announcements or other contemporaneous disclosures.
Where a company explicitly discloses the length of the auditor’s tenure, the start year may also be derived mathematically from that disclosure.
For example, if a 2025 annual report states that the auditor has served for ten consecutive financial years, the beginning of the relationship can be calculated from the disclosed tenure period.
Big4News uses this method only where the underlying tenure disclosure is explicit enough to support the calculation. We do not estimate auditor tenure based simply on the earliest annual report we happen to locate.
Where a reliable start year cannot be established, the field is left blank rather than guessed.
Audit fees
The audit-fee field is intended to capture the amount paid for the external statutory audit.
Where companies separately disclose fees for:
audit services;
audit-related services;
tax services;
advisory work; and
other non-audit services,
Big4News uses the audit-services fee wherever possible.
Where a company does not disclose a clean standalone audit-services figure but reports an audit or closely related statutory-assurance category, the closest clearly identified equivalent may be used.
Non-audit consulting and advisory fees are not intentionally included in the audit-fee figure.
Because disclosure practices vary significantly between jurisdictions, audit-fee comparability is not always perfect. Readers should therefore treat the figures principally as company-level disclosures rather than as a completely standardised accounting measure across every market.
Currency
Audit fees are generally reported in the currency used by the company in its financial statements.
For datasets where a common currency materially improves comparability, Big4News may convert fees into a single currency.
Where conversion is used, this is stated on the relevant page.
Currency conversion does not change the underlying source figure and is used solely to allow more meaningful comparison within the dataset.
Joint audits
Some jurisdictions require or commonly use joint statutory audits.
Where two audit firms jointly audit a company, both are recorded rather than assigning the engagement to a single firm.
Where sufficient information exists, Big4News also records the start year of each auditor separately.
Market-share calculations for joint-audit markets therefore require different treatment from markets in which each company has a single statutory auditor.
Any such differences are explained on the relevant page.
Auditor rotation and firm changes
A change in signing partner is not treated as a change in audit firm.
Similarly, internal reorganisations or changes in the legal name of a member firm do not automatically reset the audit-tenure calculation where the underlying audit-firm relationship has clearly continued.
Where a merger, network change or transfer between legally distinct audit firms creates genuine ambiguity, Big4News examines the underlying history before deciding whether the engagement should be treated as continuous.
Dataset composition
The companies included in a Who Audits? dataset depend on the scope of the individual project.
For stock-market indices, constituent lists change over time as companies are added, removed, merged or delisted.
For thematic datasets — such as the largest companies in a particular sector — the population may depend on criteria such as market capitalisation, revenue, geography or another stated ranking methodology.
Each Who Audits? page therefore represents the relevant company population at the time the dataset was compiled or most recently updated.
Where necessary, the individual page explains the criteria used to determine which companies are included.
Market-share calculations
Unless otherwise stated, market share is calculated by the number of companies audited, rather than by company revenue, market capitalisation or audit fees.
For example, if PwC audits 30 companies in a dataset containing 100 companies, its market share is reported as 30%.
Where every company has one auditor, the resulting percentages should total approximately 100%, subject only to rounding.
Joint-audit markets may require a different denominator or presentation, which is explained on the individual page.
Missing data
A blank field means that Big4News has not identified sufficiently reliable public evidence to populate the field.
Historical auditor tenure can be particularly difficult to establish because older annual reports are not always available online and regulatory archives differ substantially between jurisdictions.
Similarly, some companies disclose auditor remuneration only at group level or within broader categories that make a standalone audit fee difficult to isolate.
In those circumstances, Big4News leaves the field incomplete rather than introduce an unsupported estimate.
Corrections and updates
Public-company disclosures can change, historical records can surface and mistakes are possible.
Big4News therefore treats Who Audits? as a living research project rather than a static database.
If you identify an error or have primary-source evidence that would improve an entry, please contact Big4News on info@big4newscom with the relevant company, data point and supporting source.
Corrections supported by reliable evidence will be incorporated into the dataset.
Who Audits? is an editorial research project produced by Big4News. The data is compiled from publicly available sources and should not be treated as investment, legal or accounting advice.
Who audits the world’s largest companies?
Explore the Big4News Who Audits? hub, which maps the audit firms behind the world’s leading stock-market indices — including auditor tenure, audit fees and Big Four audit market share.