Dollar Thrifty Automotive Group Inc., posted third-quarter profit that missed expectations by a wide margin, hurt by a 20 percent increase in vehicle depreciation costs and lower-rental day volume growth, sending the shares down by about 10 percent.

The company also cut its full-year earnings forecast for the second time in three months on slower-than-expected revenue growth and a delay in vehicle shipments from its primary supplier.

Vehicle depreciation costs equaled about 27.4 percent of the company's total revenue in the latest quarter, compared with 25.3 percent a year ago.

However, the company expects these cost increases to moderate as it begins to buy 2008 model vehicles.

Third-quarter profit almost doubled to $11.3 million, or 48 cents a share, compared with $5.9 million, or 24 cents a share, for the year-ago period.

Total revenue rose 7.7 percent to $522.0 million.