NEW YORK — Investors like to cheer when stock buybacks are announced, but they might want to hold their applause until they see how companies plan to pay for them.

Many companies are borrowing money to finance their buybacks, instead of using the cash they have. As long as that debt remains cheap and plentiful, it won't affect profits.

Credit conditions are quickly deteriorating now, making debt-laden buybacks much more expensive. At least in the case of Expedia Inc., the rising cost has run one repurchase plan completely off its intended course.

Companies like to spin buybacks as positive news, saying repurchases "enhance shareholder value" since they tend to boost stock prices and earnings per share by reducing the supply of stock outstanding.

For six straight quarters, there has been an unprecedented $100 billion or more in stock repurchased by Standard & Poor's 500 companies, according to S&P. That is twice the amount that S&P 500 companies have paid out in dividends.

The overall stock market has benefited as a result, with buybacks and buyouts providing the main fuel for the record run in share prices over the last year.

But a spoiler to the buyback boom could be the recent debt-market turbulence. The troubled subprime mortgage market has imploded amid rising defaults in home loans among borrowers with weak credit. Lenders have reacted by raising interest rates or asking for other protections to guard them against risk.

Suddenly, the free-flowing liquidity that fueled so many buybacks is fading fast.

Expedia already got caught in that down draft. On June 19, it announced plans to repurchase about 116.7 million shares, or about 42 percent of its outstanding stock, for as much as $3.5 billion. Since it only had $637 million in cash at the end of the first quarter, that meant much of the buyback would be financed with debt, according to credit research firm Gimme Credit.

Only weeks later, on July 23, the Bellevue, Wash.-based company slashed its buyback plans to 25 million shares, or about 8 percent of shares outstanding, citing conditions in credit markets for its decision. The company's shares, which had jumped 14 percent on the buyback announcement in June, plunged 9 percent.

Analysts at Morgan Stanley estimate that the likely cost of its new debt went up 100 basis points, or 1 percentage point, in a matter of weeks, which would have made it highly dilutive to earnings.

Kimberly-Clark Corp. faced a tough sell with its $2.1 billion investment-grade debt offering last Wednesday to help finance its $2 billion share repurchase.

Craig Hutson, an analyst at Gimme Credit, said that Kimberly-Clark made a "rare show of either bravery or stupidity" in its decision to test the debt markets last week. But the deal did go through.

For that to happen, the Dallas-based consumer products company had to sweeten its offer. The yield on its debt was pushed up to 6.625 percent compared with 4.95 percent on the 30-year Treasury bond, giving it a 167 basis point spread. A month ago, that spread could have been 40 basis points less, according to Sid Bakst, senior portfolio manager at Robeco Investment Management.