The study by the Society of Local Authority Chief Executives & Senior Managers compares council chief executive pay to a post in the private sector overseeing similar annual turnover and number of staff.
It reveals that the gap differs widely with some council chief executives earning barely a quarter of an equivalent boss in a private firm.
The average district council chief executive gets £78,104 whereas the head of Millie's Cookies receives £246,000. The mets pay their chief executives an average of £116,400 compared to Wolverhampton and Dudley Breweries' boss's salary of £454,000.
The findings come despite record rises in chief executive pay in recent years. Kent CC's Mike Pitt, believed to be the best paid chief executive in the country, gets £180,000 a year - nearly £5,000 more than prime minister Tony Blair.
And the next chief executive of Bradford MBC could hit the £200,000 barrier after the council advertised the post for £50,000 more than the last incumbent got.
But the GMB said some of the pay rises chief executives had received were unfair as they dwarfed the settlement worth up to 7.7% and 11% over two years offered to local government workers last September.
A spokeswoman said it was reasonable in the context of what private firms pay that a typical chief executive in local government now earns close to £100,000.
'But we are worried by some of the pay rises being given,' she added.
Mike Bennett, Solace's assistant director general, said: 'Chief executives now have more responsibility and power. The job requires highly skilled people and the pay reflects this.'
How Public/Private Pay Compares
Type of council (ave rage salary)
London boroughs £116,400
Private company equivalent
Compass Services UK and Ireland £271,000
Wolverhampton and Dudley Breweries£454,000
Blockbuster Entertainment £416,000
CP Holdings £462,000
Millie's Cookies £246,000
Shire districts £78,104