WASHINGTON — All those speculators getting the blame for driving up the price of oil these days — just who are they? For part of the answer, look in the mirror.

The retirement savings of workers across the country, entrusted to pension-fund managers, are being plowed into one of the few investments that has delivered phenomenal returns in recent years.

For decades, futures contracts were mostly traded by commodity producers and the people who used the actual products, such as crude oil, corn and soybeans. Agreeing to a price today for a commodity to be delivered in, say, two months is a way to smooth out price fluctuations for those supplies.

But large investors faced with the threat of inflation have increasingly used them as protection against the falling dollar. That includes pension funds, along with investment banks, mutual funds and private hedge funds.

Research firm Ennis Knupp and Associates says $139 billion had been funneled into energy commodities, primarily crude oil, by the end of March — and the firm estimates more than half of that is from retirement money.

The investments have paid off. The Standard & Poor's GSCI index, which tracks a basket of commodities, is up 19 percent in the past five years, compared with just 9 percent for the S&P 500 stock index.

The risk is that if the remarkable run in oil and other futures markets reverses course, billions of dollars of retirement benefits could be wiped out.

"A pension fund is supposed to be investing money in secure, stable investments for the benefit of the people whose money they are investing," said Dan Lippe, an energy analyst at Houston-based Petral Consulting Inc.

"When we hit that wall and things start falling," he said, "they will fall very fast, and the pension funds that invested in commodities will see a tremendous loss of value."

The retirement system for public employees in California, the largest in the nation, has $1.3 billion invested in commodities. Most of it tracks the S&P commodity index.

That's still just one-half of 1 percent of the fund's total $240 billion in assets, said Michael Schlachter, who advises the California pension fund. He said a collapse in oil or other commodity prices would have little effect on retirees.

Still, a growing chorus of experts is convinced retirement investments are enough to distort prices.

Billionaire George Soros, the airline industry and the International Monetary Fund are all pressuring Congress to curb speculation by large investors. Democrats in Congress say they hope to vote on restrictions by August.