PWC
From Exxon's official webpage states: "Independent, registered auditors PricewaterhouseCoopers LLP..." So, PWC is the auditor.
deloitte
KPMG
The firm Deloitte & Touché LLP is the independent auditor for Twitter. They handle all of the financial statements for this company.
Deloitte & Touche LLP
PricewaterhouseCoopers, LLC
Auditor's judgement
As of their 2011 annual report, it is PricewaterhouseCoopers.
An independent auditor is asked to express an opinion on the fair presentation of financial statements because a company may not be objective with respect to its own financial statements.
aaron barry berry
163-acers