WASHINGTON (AFP) - Pay for chief executives of US companies has soared nearly 10-fold over the last 35 years to an average of US$15.2 million (S$18.98 million) in 2013, according to a study released on Thursday.

Total compensation, including bonuses and stock options, jumped 937 per cent since 1978, said a report by the non-partisan Economic Policy Institute (EPI), which is partially funded by labor unions.

The ratio of CEO pay to that of average workers rose from 29.9-1 in 1978 to 295.9-1 in 2013, the study said.

"The economy is recovering for some Americans, but not for most," the report said.

"Those at the top of the income distribution, including many CEOs, are seeing a strong recovery while the average worker is still experiencing the detrimental effects of a stagnant labor market."

EPI tied the shifts in CEO compensation to the fortunes of the stock market.

Average CEO pay fell from US$18.5 million in 2007 to US$10.4 million in 2009 as the stock market slumped amid the financial crisis, before gradually rising each of the last four years as US equities have risen.

This trend means CEO pay "often grows strongly simply when the overall stock market rises" and does not necessarily reflect improved performance, EPI said.

Policy ideas proposed in the report include raising taxes on the wealthiest and removing tax incentives that promote stock options.

The report comes amid a growing debate in the United States on economic inequality following the recent publication of Thomas Piketty's bestselling book, "Capital in the Twenty-First Century".

President Barack Obama has championed a hike to the minimum wage, as has EPI.