As of October 27, gold prices were hovering around $1,747 per ounce. The yellow metal's valuable cousin, on the other hand, was selling for about $1,636 an ounce.

And I don't mean silver. I mean platinum.

When you look at those two prices together, it takes just 0.93 ounces of gold to buy an ounce of platinum. Or, looking at it from the other end, you could trade one ounce of gold for 1.07 ounces of platinum.

Gold hasn't been worth more than platinum since 2008. Before that, you have to go back to January 1992 to see the last time the yellow metal traded this far above parity to the white one.

Put simply, platinum prices relative to gold are at their cheapest level in nearly 20 years.

This has been a one-sided relationship throughout the years. Platinum almost always has the upper hand over gold, in terms of price. That's to be expected, considering platinum is about 30 times rarer. Annual platinum production is just a tiny sliver compared with that of gold.

[Gold supplies have been squeezed as well, with demand rising 24% in 2010 compared to supply growing only 2%. See the 4 Factors That Made Gold This Decade's Best Investment] 

That's what makes this such an odd occurrence.

The last time it happened was December 2008, when gold was soaring as a safe haven, just as weak auto sales were sapping demand for platinum (which is used in catalytic converters). In that particular case, platinum retook gold just a few days later and went on to post a powerful 130%-plus gain during the next two years.

This time around, the extreme ratio has persisted for a couple months. It's not so much because platinum prices have nosedived (they're down about 9% for the year), but rather because gold is in the 11th year of a bull market and continues to soar. Prices of gold have climbed another 25% since the start of the year.

On Jan. 1, it took 1.25 ounces of gold to buy one ounce of platinum. That ratio of exchange has now slipped all the way below 1:1. This is more than just a statistical abnormality...

As you can see from the chart below, we've been in unprecedented territory.

Platinum has traded about 64% above gold on average during the past decade. Based on this, and with gold at $1,747 an ounce, you might expect platinum to have surged above $2,800 an ounce. Instead, it has sunk below $1,650.

Personally, I think it's the latter. Speculators might consider this an opportune time to enter a pair trade by going long platinum and short gold.

This would remove any outside influences and just capture the performance of one metal against the other.

This strategy has a high probability of success because there's no reason for platinum to be below gold. But I'm not a trader, nor am I betting against gold.

I think the better solution for long-term investors is to simply overweight platinum -- and not just because a chart tells them to. 

[Don't bet too heavily on gold just yet: 2 Big Reasons I think Gold Could Continue to Tumble] 

The Investing Answer: Platinum group metals (PGMs) are irreplaceable and will remain in high demand. Auto production is expected to rise, which should boost demand. There are looming strike threats in South Africa, home to 80% of the world's supply. As my colleague David Sterman recently pointed out, the world's other major producer, Russia, has warned that output will begin falling.

You won't find any publicly-traded U.S. platinum companies. But First Trust has conveniently packaged all of the world's top suppliers in one place. For a modest annual cost of just 0.70%, the First Trust ISE Global Platinum fund (Nasdaq: PLTM) offers a diverse global basket of 24 major producers, including well-positioned leaders such as Impala Platinum and Anglo Platinum.

The exchange-traded fund (ETF) was punished during the selloff and was down nearly 50% for the year before a strong rally in October. But I still think this in an opportune entry point for long-term investors.

There are gold and silver ETFs you can invest in too: The SPDR Gold Trust ETF (NYSE: GLD) tracks gold prices and iShares Silver Trust ETF (NYSE: SLV) follows silver prices as well.

[Also check out our silver investing guide: My Favorite Ways to Own Silver Today]