The two firms have been jockeying for top spot in recent years, in 2015 PwC seized the control after two years of playing catch-up, but last year Deloitte powered ahead.
EY also further extended its lead in third over KPMG, with a strong 6% rise in revenue growth to $31.4bn (£22.34bn), according to the latest global network rankings from International Accounting Bulletin.
However KPMG still enjoyed an increase of 4% to $26.4bn (£18.78bn), despite a difficult year in which it received criticism over its audit of Carillion, saw its entire leadership team resign in South Africa and has three partners in the US standing trial.
Meanwhile, the gap between the Big Four and the rest shows no sign of closing. In fifth spot BDO’s revenues jumped 7% to $8.13bn (£5.78bn). RSM, in sixth, rose 5% to $5.09bn (£3.62bn) and Grant Thornton increased revenue 4% to $5bn (£3.56bn).
Overall it was a strong year for the profession globally as every firm in the top 10 recorded growth and only three of the top 30 firms saw a drop in income.
Outside of the top 10, PKF International saw the largest increase with a boost of 25% to $1.29bn (£0.92bn)
The top 10 in full:
1. Deloitte - £27.67bn
2. PwC - £26.81bn
3. EY - £22.34bn
4. KPMG – £18.78bn
5. BDO - £5.78bn
6. RSM - £3.62bn
7. Grant Thornton - £3.56bn
8. Crowe Horwath International - £2.71bn
9. Nexia International - £2.58bn
10. Baker Tilly International - £2.42bn
The big firms continued to increase their workforce last year – with the Big Four employing almost one million people globally combined. EY boosted its head count by 7% to more than 230,000 and Deloitte added 8% to its workforce for a total of 263,924.
Baker Tilly International significantly increased its staff numbers by 10% to 33,600, while Mazars enhanced its by a fifth to more than 20,000 globally.