Strong sales at stores in the U.S. helped Costco Wholesale post a 5 percent increase in a key revenue metric for July. But the stronger dollar and lower gas prices pressured its results.

Revenue at stores open at least a year is a key indicator of a retailer's health because it excludes results from stores recently opened or closed.

The Issaquah-based wholesale club operator said Wednesday that revenue at U.S. locations open at least a year climbed 7 percent for the period ended July 29. The figure was flat for its international stores.

Taking out the impact of lower gas prices and a stronger dollar, revenue at stores open at least a year rose 7 percent for the month. In the U.S., the metric climbed 8 percent while overseas it gained 7 percent.

When the U.S. dollar is rising against the world's other currencies, companies that sell goods internationally take a hit when converting revenue in foreign currencies back into the dollar.

Total revenue for July increased 8 percent to $7.25 billion from $6.74 billion.

For the year to date, Costco's revenue at stores open at least a year climbed 7 percent. Stores in the U.S. posted a 7 percent rise in the figure and international locations recorded a 6 percent increase.

Removing the impact of higher gas prices and the strong dollar, revenue at stores open at least a year gained 6 percent. The figure climbed 6 percent for U.S. locations and 9 percent internationally.

Total revenue climbed 9 percent to $87.71 billion from $80.18 billion.

Costco runs 605 warehouses, including 438 in the U.S. and Puerto Rico, 82 in Canada, 32 in Mexico, 22 in the U.K., 13 in Japan, eight in Taiwan, seven in Korea and three in Australia.