Automatic enrolment could more than double the numbers saving in DC schemes by 2030, according to the Pensions Policy Institute.
The institute has published a report which found that the vast majority of new private sector pension savers arising from automatic enrolment are likely to be saving in Defined Contribution workplace pension schemes.
Daniela Silcock, senior policy researcher, said: "Based on reasonable assumptions about opt out rates, we could see up to 15 million people actively saving in private sector workplace schemes by 2030, with up to 8.5 million of these newly saving, and up to £495 billion in DC assets.
"This is a phenomenal change to the pensions landscape when you consider that without automatic enrolment there might be around 6 million DC savers and £350 billion in DC assets by 2030."
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The current rate of opt-out is around 9-10% on average, but this could grow as small to medium sized employers start to automatically enrol their employees and as minimum employee contributions rise.
The report stated that if the opt-out rate from automatic enrolment stays at 9%, 8.5 million people could be newly saving in a pension by 2030 and there could be 15 million people actively saving into private sector workplace pension schemes in total, the vast majority of these in DC schemes. However, it added that if opt out rates rise to 25%, there might only be 6.5 million new savers in 2030, out of a total of 13 million private sector workplace pension active savers.
Under these different opt out scenarios, by 2030 the value of assets in private sector DC workplace pension schemes could range between £455 billion and £495 billion (2014 earnings terms) compared to around £350 billion without automatic enrolment.
The value of total private sector workplace DC assets in the UK could become greater than the total value of private sector workplace DB assets in around 2036.
Ms Silcock said: "The current opt-out rate of 9%-10% has exceeded expectations, however it is worth reflecting that larger employers, who are more likely to have existing provision and extensive HR and admin support structures around pension saving, have just completed their staging dates.
"Small to medium sized employers will be reaching their staging dates over the next few years, and it will be important that these employers are given the support necessary to fulfil their duties and that employees for whom pension saving might be beneficial are not encouraged to opt-out."