* May comparable sales up 9 pct vs ests of 9.7 pct
* Says May sales helped by extra day from holiday shift
- Costco Wholesale Corp said it saw May sales in stores open at least a year rise 9 percent, slightly less than Wall Street forecasts for the period, which included an extra day compared with a year ago due to the shift in the Memorial day holiday.
Analysts had expected the largest U.S. warehouse club operator to post sales of 9.7 percent, according to Thomson Reuters data.
For the four weeks ended May 30, the company said its net sales rose 11 percent to $6.09 billion from the previous year.
The shift in the Memorial Day holiday, which fell on May 31 this year, helped the May 2010 total and comparable sales by about 2 percent, the company said.
Including the benefit from the inflation in gasoline prices and strengthening foreign currencies, Costco said same-store-sales at U.S. locations climbed 7 percent, while international sales jumped 17 percent.
Shares in the Issaquah, Washington-based company closed at $58.95 Wednesday on Nasdaq.
(Reporting by Antonita Madonna Devotta in Bangalore; Editing by Greg Mahlich)