Orange County, California’s $11.5 billion pension is putting together a fund open to smaller retirement plans to give them access to private-equity investments at a lower cost.

The county today selected London-based Pantheon Ventures LLP to manage the pool. For the past 10 months, Orange County’s Employees Retirement System has been collaborating with other California pensions to develop the fund, which would give them more leverage when negotiating fees with private-equity firms.

Orange County, south of Los Angeles, plans to invest $50 million to $100 million annually over three years. It may save as much as $5 million a year in fees, more than the retirement system pays investment staff, according to a memo released today. Pensions from California’s San Bernardino County to the state of Wyoming are considering joining the fund, according to officials at both plans.

“We’ve demonstrated the effectiveness of collective purchasing and economies of scale,” said Girard Miller, chief investment officer of the Orange County system. “The pension fund beneficiaries, stakeholders and taxpayers are all going to benefit as a result of today’s decision.”

U.S. public pensions from California to Connecticut have piled into riskier investment such as private equity as they face a $800 billion funding gap on promises to retirees amid slow growth and low interest rates.

Expensive Chase

Private-equity firms use borrowed money to buy companies, improve profits and resell them. The top 25 percent private-equity funds delivered better returns than the Standard & Poor’s 500 stock index by 37 percent over the life of the fund, according to a 2011 study that looked at 450 buyout funds from 1984 to 2010.

Chasing those returns is expensive. Private-equity and hedge-fund managers typically charge 2 percent of assets they oversee, plus 20 percent of profits. Some small and mid-size pensions that are shut out of the funds with the best track records buy stakes in a pooled investment called a fund-of- funds, which creates another layer of fees.

“Most of these guys can only write $5 million checks,” said David Fann, president of TorreyCove Capital Partners, a San Diego-based firm that advises pensions on private-equity funds. “They’re very low on the list of priority investors. They just don’t have meaningful buying power.”

Money-management fees paid by Orange County, which has a 5 percent allocation to private equity, have more than doubled to $40 million over the last decade, according to the pension’s annual reports.