Ever wonder what's in the wallets of the ultra rich (besides a lot of money)? One answer: some exclusive credit cards that few people know about. Even some of the world's richest people don't qualify for all of these cards.

Of course, the companies that offer these cards aren't printing mailers that disclose all of the details. These cards are by invitation only and for many of them, you won't find a webpage highlighting their features. Here's what we know about some of the most exclusive credit cards in the world.

You may know it as the black card. Go to the American Express website and all you will find is a small picture of the card with the required disclosure statement. This invitation-only card requires that you have been a platinum card holder for at least one year and have spent a minimum of $250,000 over the past year. Some reports say that you need to make about $1.3 million per year and have a net worth of around $16 million.

Perks of the card include access to the very exclusive Centurion lounges located at select airports; platinum status on Delta and US Airways; 24/7 concierge service that is rumored to get you a table at any restaurant, any airline seat or any extravagant request you may have. About the only things American Express will disclose officially are the $7,500 initiation fee, the $2,500 annual fee per card and all the other required disclosures.

If you're an astute AmEx watcher, you probably noticed that most of the benefits of the Centurion are available with the much less expensive and exclusive platinum card (see Using Platinum AmEx Benefits). But along with the status of having the Centurion card (made of titanium, by the way), those lounges and that extra attention could be worth it to someone.

If you're among the 1% of the 1% – and you're in the market for an ultra-rich card – you probably won't look much further than the Centurion. But how about a card made of 24-carat gold and palladium? According to one estimate, just the physical card from JP Morgan is probably worth at least $1,000. What kind of 24-carat perks does it deliver?

You don't get the card for the two points for every dollar spent on travel or one point everywhere else that it delivers. You may not even care about the extra points you get after spending $100,000 in a single year. What does make the big difference could be the concierge service – that person who will get you tickets to anything and (as the benefits guide is rumored to say) the virtually limitless array of unique offers, time-saving conveniences and personalized insider expertise.

To get this card, you have to be a JP Morgan Private Bank client (or a Chase Private Client or similar-level JP Morgan Chase customer) only.

According to Dubai First, Royale Card is the region's first diamond-embedded World MasterCard that redefines the standards of luxury. It is available by invitation only and is bespoke for a select group of people representing royalty and the upper echelons of the social and business community.

Are you royal or in the upper echelons? Most people would say no – but if you are, you might qualify for this card, which has gold trim on the left and top of the card and a .235 carat diamond in the center.

There is no credit limit and, according to an official at the bank, if you ask for the moon, they try to get it. The card comes with a team of lifestyle managers who are available 24/7 – even, presumably, if the diamond falls out of your card.

This card is equivalent to the JP Morgan Palladium card. Only available to Citi's private banking clients, the card comes with a $500 annual fee and many of the same perks you're used to seeing with ultra high-end cards. Expect access to exclusive airport lounges, travel upgrades, a personal concierge and more.

People rarely achieve ultra-elite status by being snowed by luxuries with insufficient payback. When these banks offer you their ultra-exclusive, secretive cards made of materials sure to add extra weight to your wallet, you will, of course, compare them to what you already have. Are these cards truly better? How much more, if anything, do they cost and are the benefits the kind that would add to your life? For more comparisons, read Chase Sapphire Preferred Vs. AmEx Platinum and The Best Credit Cards For Airport Lounges.

On the other hand, you could ask the marketers to let you test their concierge capacity by flying you to some faraway land where you can consider their offer in the solitude of exclusivity as a team of personal chefs and masseuses pamper you. Then you will know if the service is really as good as they say.