If you have a credit card with a variable interest rate, I'm sure you have noticed your rates have been going up.

The average standard rate at the beginning of this month was 14.13 percent, a 27-month high, according to Bankrate.com. The average gold and platinum variable rates were 13.18 percent and 11.12 percent, respectively.

Fixed credit card rates were unchanged over the past month, with the average standard rate remaining at 12.75 percent, Bankrate.com reports. The average gold and platinum fixed rates were still 13.09 percent and 11.64 percent, respectively.

But does fixed always mean you're safe from interest-rate increases?

Please. We are talking about credit card practices here. Just because you have a credit card with a fixed rate doesn't mean it will stay that way.

You may be surprised to learn that buried in your credit card agreement is language giving your card company the right to raise your rate for any number of reasons.

Like what? you might (or should) ask.

Some will raise your rate if you start running up your other credit cards. Your rate could also go up if you fail to make more than the minimum monthly payment on your account.

Companies are looking out for folks who aren't perfect credit users.

For example, let's just say you've been late on payments for one credit card. You're having a little financial trouble, but you make sure to pay another credit card bill on time.

Ah, but that thinking could get you in trouble with the credit card company you have been paying on time and as agreed. Some companies routinely check the credit history of their customers and will automatically hike a customer's interest rate if he or she misses a payment on another card.

That's not all.

Let's say you transfer the credit card balances from several cards to one offering zero-percent interest for six months. Could be a great deal -- if you never, ever miss a payment or pay late.

If you do, be prepared for the possibility of a skyscraping rate hike.

Didn't know all this could happen? Well, you aren't alone.

In fact, the Office of the Comptroller of the Currency is so concerned about what it called unfair or deceptive credit card offers that it issued an advisory letter recently warning national banks about certain credit card marketing and account-management practices.

The OCC said three practices in particular are troublesome:

* Solicitations for credit cards that advertise credit limits "up to" a maximum dollar amount, when that credit limit is, in fact, seldom extended. For instance, you may get an offer trumpeting that you could be eligible for a credit limit of up to $20,000. You excitedly apply, but lo and behold the bank says you qualify for only a $1,000 credit limit. Your dreams of buying a flat-panel television are dashed.

* Using promotional rates in credit card solicitations without clearly disclosing the significant restrictions on the applicability of those rates.

* Increasing a cardholder's annual percentage rate when the circumstances triggering the increase have not been disclosed fully or prominently.

"These practices may entail unfair or deceptive acts or practices," the OCC said in its letter.

You think?

Actually, most of you don't have to think about it. It's totally unfair and deceptive to bury important details about a credit offer in fine print.

Anyway, I think what the OCC told the banks could be useful to consumers. Here's what the agency said banks should be doing:

* When sending out solicitations with "up to" credit-line hype, provide applicants with a "default credit line" (the lowest credit line available). In other words, the agency encouraged banks to be up front and tell folks they may qualify for only a certain amount and that amount could be significantly lower than the maximum advertised.

* Disclose fully and prominently any material limitations on the promotional rate, such as the time period for which the rate will be in effect. The OCC also wants credit card companies to be clear about any and all circumstances that could shorten the promotional rate period.

* Disclose fully and prominently in promotional materials the circumstances under which the credit card agreement permits the bank to increase the consumer's interest rate (other than because of a variable-rate feature).

All of the OCC recommendations should be common practice. But I know they're not. So it may be up to you to look for the details -- even if you have to look on the back of the offer letter at the very bottom in type that makes your head hurt when you try to read it. But do it.

Especially look for the loopholes. If you do, more often than not you may decide the credit terms are too restrictive to make it worth your while.

Michelle Singletary discusses personal finance Tuesdays on NPR's "Day to Day" program and online at www.npr.org. Readers can write to her at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or send e-mail to singletarym@washpost.com. Comments and questions are welcome, but due to the volume of mail, personal responses may not be possible. Please also note that comments or questions may be used in a future column, with the writer's name, unless a specific request to do otherwise is indicated.