Anyone watching the parabolic rise in commodity prices the last six months has got to be wondering what’s going on.

Crude oil seems to set a record every day. The price of rice, which did nothing for two decades, more than doubled in the past year. Wheat prices are up 90%; soybeans 50%. Copper prices are up 26% since the start of the year as housing, a major consumer of the metal, implodes.

Yes, I know. I’ve read the explanations about soaring demand for raw materials from countries like China and India and increased investor appetite for “real” assets as a hedge against the falling dollar and rising inflation.

The thing is, “real consumers change habits gradually,” the president of Marketfield Asset Management and chief investment strategist at Oscar Gruss & Son Inc., Michael Aronstein, said.

Did normally forward-looking markets just realize that China and India are industrializing, with their populations of a billion-plus each eating and living better? Has the global economy’s need for crude oil really increased by one-third since the start of the year? Oil prices rose almost $12 last week alone.

If it’s not real demand to heat our homes, power our factories, and feed our population, then could it be, might it be, a bubble? And if it is, are the commodity markets looking at the same fate as the Nasdaq Composite Index in 2000-2002 and the housing market at present?

“It looks like an old-fashioned corner to me,” Mr. Aronstein said.

With other asset classes, there are metrics that allow us to quantify the degree to which prices have strayed from their fundamental moorings. Stock prices have an historical relationship with underlying earnings. House prices don’t stray too far from their “earnings” stream, or rental value.

With commodities, no such quantifiable ratio exits. Instead, analysts point to verticality, or the rate of price increases in a short period of time; to the fact that open interest in futures contracts dwarfs actual supply; or to the sheer volume of trading. Last week, the average daily volume of crude oil contracts on the Nymex was almost eight times daily oil demand.

Some of the standard gauges for measuring speculation in commodity markets have been rendered useless by the changing nature of the participants.

For more than four decades, the independent futures and options markets regulator, the Commodity Futures Trading Commission, has been detailing futures positions of hedgers (commercials) and speculators (non-commercials) in its Commitment of Traders report. Hedgers are those traders who are engaged commercially in the cash market — farmers, for example — and use the futures markets to hedge their production.

With the popularity of long-only commodity index funds and the prevalence of total-return index swaps, the definition and quantification of speculation has changed, according to the president of Bianco Research in Chicago, Jim Bianco.

Let’s say a pension fund, like the California Public Employees Retirement System, wants to increase its exposure to commodities. Calpers, a speculator according to the CFTC, does a total-return swap with Goldman Sachs Group Inc., a hedger.

Goldman promises to pay Calpers the total return on the Goldman Sachs Commodity Index and hedges the swap by buying futures contracts. Calpers’s speculative bet on commodities gets recorded as Goldman’s hedging in the COT report. In so doing, investors circumvent the position limits on non-commercials, Mr. Aronstein said, who estimates that passive commodity index exposure in commodities amounts to some $250 billion.

With everyone on board the express train, pension funds can market these bets as “asset diversification.” And who will argue otherwise in the middle of a boom?

Last year, the CFTC began publishing a new supplemental report on commodity index traders in 12 selected agricultural commodities. The new category includes the positions of managed and pension funds as well long dealer positions to hedge their swaps with pension funds.

According to Mr. Bianco’s analysis, index positions accounted for 41.3% of the total market capitalization of the covered markets as of May 2. These funds “are the largest participants in the markets covered in this report, dwarfing positions held by both non-index hedgers and traditional speculators,” Mr. Bianco said.

To be sure, there are external forces creating seismic shifts in commodity markets. The government’s ethanol mandates (as a gasoline additive) and tax incentives to ethanol producers are boosting demand for corn, creating ripple effects throughout grain and livestock markets. The U.S. Department of Agriculture estimates that ethanol producers will account for almost one-third of the 2009 corn harvest.

“We don’t want to admit we’re using corn and cooking oil to drive our cars,” Mr. Aronstein said. “All these idiotic things politicians do have real and devastating consequences. It used to be that they were just wasteful.”

Mr. Aronstein ran a long-only commodities fund in the mid-1990s before seeing the light.

“If you want to be in commodities, buy a process, not a product,” he said. “Own a gas company. Or a forest products company. Buy an entity that extracts value. And you get a free option: the product might appreciate.”

The history of investors buying assets — from tulips to tech stocks — because the price is going up is in agreement on one point: People end up holding a lot of stuff they don’t want.

But hey, with lots of vacant homes on the market right now from the last burst bubble, these folks might be able to score some storage space on the cheap.

Ms. Baum is a columnist for Bloomberg News.