You park your car at the gym. After your workout, you walk out… and it's gone. Not your car. Not your stereo. Not your radar detector. What's gone is your catalytic converter. And you'll know it the moment you start your car. It'll sound like a Harley just pulled in next to you.

Catalytic converters have become a hot commodity for thieves. How bad is the problem? It's national in scope. On Saturday, NPR interviewed a spokesman for the National Insurance Crime Bureau on the subject. And you can even buy a security system just for your converter!

What's the attraction? The small amounts of platinum and palladium in a converter. Thieves can sell the converters for $20 to $200 apiece to recyclers. And you'll be out a grand or more to replace the one in your car.

This rash of catalytic converter thefts, says Andy Gordon, puts a spotlight on the coming bull market in platinum and palladium.

200% plus gains

Andy sees stellar gains ahead. Platinum is one of the rarest metals in the world. It is so rare that all of the metal ever mined would fill a room less than 25 feet square. Palladium is another rare PGM (platinum group metal). It is similar to and less expensive than platinum.

As with all commodities, we need to look at supply and demand.

Supply has been declining

Around 75% to 80% of the supply of these metals comes from South Africa, and there are only 10 significant platinum mining companies. One of the 10 is Platinum Australia Limited (ASX:PLA). John Lewens, managing director of PLA, says production in South Africa over the last three years has declined. He says the declines have been caused by mine closures and cutbacks on capital expenditures.

Another reason is that in 2008, thanks to the global economic meltdown, the price of platinum dropped dramatically, as you can see.

When commodity prices drop, producers usually cut back production. And when a commodity goes up in value, they typically increase production.

Take oil for example. When prices get high, old wells are uncapped. And every effort is made to get as much oil as possible out of existing wells.

That's not true for platinum. The supply is inelastic. It may take as long as seven years to get a new mine up and running. And it's estimated that 7 to 12 metric tons of ore must be mined to produce one ounce of platinum. Not only that, but the refining process is so complex it can take up to six months.

So as prices start to increase, it takes a long time for supply to catch up. And that's why Andy is so excited about the profit potential in platinum and its cousin, palladium.

Demand is increasing

The demand for platinum is primarily industrial. It comes from electronic, glass, chemical, spark plug, and fuel cell manufacturers. Only 20% of platinum is used in jewelry. But the biggest demand driver for platinum, by far, is catalytic converters. They typically account for 50% of demand.

Here’s the thing. No matter where a car is made or sold, it has a catalytic converter. And each catalytic converter contains several hundred dollars' worth of platinum and/or palladium.

And auto sales have rebounded not only in the United States but around the world. The production forecast? Check it out:

The last time an auto buying binge like this occurred was in 2000-2006, and the price of this metal increased by 2.75 times.

In 2008, worldwide demand for everything faltered. And the companies that require platinum for manufacturing stopped buying. They were content to deplete their existing inventories. Now they are restocking. Which is sure to drive up prices.

Where to invest

The best way for you to participate in the coming bull market in platinum and palladium is with two ETFs.

For platinum, check out ETFS Physical Platinum Shares (PPLT). It is well off its May high of $174, currently selling for $157. It's new this year, so it doesn't yet have a lot of volume.

The play on palladium is with ETFS Physical Palladium Shares (PALL). It, too, is new this year. It's off its April high of almost $57, and currently trades around $49.