PHOTOGRAPHS BY JOSHUA LOTT FOR THE NEW YORK TIMES

Jorge Duarte, a Car-X employee in Chicago, prepared Thursday to remove an old catalytic converter for replacement on a Pontiac.

A thief can sell a stolen catalytic converter to a scrap yard for a couple of hundred dollars. The honeycomb filter inside contains platinum traces.

CHICAGO — Jose Fernandez said he decided some time ago that on his salary as a restaurant worker, he was better off without his 1996 Toyota 4Runner. He hoped to make a nice bit of cash from its sale.

Before he could do that, though, someone beat him to extracting value: A thief sneaked under the sport utility vehicle with a battery-powered saw, slicing from the Toyota’s underbelly what may be one of the most expensive small parts of the auto world: the catalytic converter, an essential emissions-control device made with small amounts of metals more precious than gold. Who knew? Mr. Fernandez didn’t.

Inside the lobby of the New Windy City Mufflers and Brakes shop, Mr. Fernandez said he had heard a rumor that catalytic converters had suddenly become the rage on the black market here, but he did not believe it until his went missing on a well-lighted North Side street.

Theft of scrap metals like copper and aluminum has been common here and across the country for years, fueled by rising construction costs and the building boom in China. But now thieves have found an easy payday from the upper echelon of the periodic table. It seems there may not be an easier place to score some platinum than under the hood of a car.

“This morning I woke up and walked out, turned the key and there was a noise like this,” Mr. Fernandez said, grumbling the trainlike roar that cars make when they are missing their converters. “And now to fix it, I don’t want to spend the money because it’s really expensive.”

The price of gold recently hit record highs, crossing the $1,000-an-ounce mark before retreating a bit. Less well publicized has been the fate of the even-more-rarefied metals platinum, palladium and rhodium, with platinum hitting recent record highs of more than $2,300 an ounce. People who may have thought their lives had nothing to do with the booming commodities market are finding out the hard way where their connection is — in their car’s exhaust system.

The catalytic converter is made with trace amounts of platinum, palladium and rhodium, which speed chemical reactions and help clean emissions at very high temperatures. Selling stolen converters to scrap yards or recyclers, a thief can net a couple of hundred dollars apiece.

Exactly how much depends on the size of the car and its converter. But even a little bit is worth a lot. Converter thefts are the quickie crime du jour, not only in Chicago, where workers in auto body shops and other experts say it is increasingly a nuisance, but anywhere cars are, which is to say basically everywhere.

“These are definitely occurring more than they have in recent memory, and why that is is definitely tied to the price of precious metals within converters,” said Frank Scafidi, spokesman for the National Insurance Crime Bureau.

Replacement converters usually start around $450. “When you start getting into the larger S.U.V.’s, it’s $1,000-plus,” said Don Tommasone, owner of Village Automotive, a car care center just outside the city. “The larger the catalytic, the more platinum. That’s the ones they’re stealing. It’s also easier to crawl underneath them. They don’t need to jack up the vehicle, they just saw it right off.”

This month in Memphis, 140 children were stuck at their day care center after thieves stole the catalytic converters from the center’s two vans. Recently in Columbus, Ohio, 25 cars in one parking lot were vandalized for their catalytic converters. And several states are working on legislation to make it harder to resell what up to now was a part little known outside the world of auto enthusiasts and mechanics.

Because stealing a converter does not involve actually breaking into a car, it often goes undetected. Alarms and other precautions, like parking in a well-lighted area, are scant defenses.

Last year in Minnesota, someone broke into the Ramsey Police Department’s impound lot and took 19 catalytic converters off the vehicles there, a spokeswoman said. The Star Tribune in Minneapolis ran this headline about the break-in: “Thieves Show How Low They’ll Go.”

Jim Lyon lives opposite a police station in the Chicago suburb of Westmont, and can see his Jeep Cherokee from his window. Still, someone got him. “They’ll probably get 150 bucks for two minutes’ work. Not bad!” Mr. Lyon said. “As soon as I realized there was precious metal inside, I knew what they were looking for.”

Legs sticking out from under a car were a tip-off this year for the Chicago police, who said they spotted a man in the Lakeview neighborhood just before he slithered from under the car and discarded a power saw along the curb. The man and three accomplices were charged with burglary and possession of burglary tools. “When will this stop?” wondered Chris McGoey, an auto theft expert.

“When they’re not worth anything any more.”

Copyright 2008 The New York Times Company. Reprinted from The New York Times, National, of Saturday, March 29, 2008.