Martin Tilley, head of technical support at Dentons Pensions, has forecast that "a third to a quarter" of Sipp providers could quit the market in the next few years.
The reason for their departure would be increased capital adequacy and regulatory requirements from the Financial Services Authority.
Mr Tilley said: "The FSA has told us we will get an increase in capital adequacy and regulatory requirements. For those firms who aren't financially strong, this will be an issue."

He said firms who were not financially strong would end up being bought out by larger firms but if the requirements were too high, firms would not be able to afford to buy smaller firms.
This could lead to weaker firms being wound up and their clients being left to find another provider.
He criticised the FSA for delaying details of the requirements, which are promised this year, and said the industry was "waiting with bated breath."
"We don't know how high the bar will be set, who would buy a Sipp provider now without knowing what the increased liability requirements will be?"
He urged advisers to do their research on the financial strength of the Sipp providers they were choosing and assess the likelihood they would be around in the next five years.