The Wall Street Journal today reports that a rapidly-increasing number of credit card offers are for variable-rate lines of credit. According to the article, over 90% of recent credit card offer mailings were for variable-rate cards, up from 60% just last year.

Fixed-rate credit cards, however, have only been as “fixed” as the bank wanted them to be:

The question is, how much does the shift to variable-rate cards really matter to consumers? In some ways, it might be good news, helping to steer people clear from the mistaken notion that “fixed rate” actually means fixed. The term as it relates to credit cards has always been something of a misnomer.

The rate is fixed “only until the issuer decides to change it,” said Greg McBride, senior financial analyst with Bankrate.com. Sure, the creditor must give consumers some notice to change the rate, but still, the rates could change.

The Credit CARD Act recently signed into law limits banks’ ability to arbitrarily raise rates on “fixed-rate” cards, so promoting variable-rate cards tied to the prime rate essentially ensures that they will automatically increase. The prime rate is currently 3.25% — the lowest point since the 1950s — so it is virtually guaranteed to not fall any lower.

As always, the lesson is to know the facts and read the fine print before signing up for a credit card or any other financial product.