The online retailer’s profit doubled in the second quarter, as revenue rose 41 percent despite consumer anxiety about the economy.

“This is a very robust performance and it clearly shows that online selling is holding up very well even if consumer confidence is lower,” said Jeffrey Lindsay, an analyst at Sanford C. Bernstein. “Even if people are buying less over all, Amazon is benefiting.”

Amazon’s report, announced Wednesday, caps a week of largely mixed results from technology companies. EBay, the online marketplace, showed that it was not immune to the slumping economy when it reported last week that auction growth was slowing, although its profit continued to grow.

Jeffrey P. Bezos, Amazon’s chief executive, said the company appeared to prosper as more customers went online to shop instead of driving to stores. “Even just driving 10 miles to the store can mean a few dollars,” Mr. Bezos said in a conference call with analysts on Wednesday. “We think consumers are taking that into account.”

Mr. Bezos also said that more customers signed up for the company’s $79-a-year all-you-can-ship program, Amazon Prime, and that the company had no plans to change Amazon’s free-shipping policy on many items, despite rising gas prices.

Amazon’s net shipping cost rose to $128 million from $75 million in the quarter a year earlier, but company executives said that revenue from shipping increased as well, to $186 million from $152 million.

Amazon reported net income of $158 million, or 37 cents a share, up from $78 million, or 19 cents a share, in the second quarter of 2007.

Operating income rose 86 percent, to $217 million, which includes a $53 million noncash gain from Amazon’s sale of its European DVD rental assets and by the effect of the weak dollar.

Revenue rose 41 percent, to $4.06 billion, from $2.89 billion in the year-ago quarter. Excluding the benefit of exchange rates, Amazon’s sales would have been roughly $3.9 billion.

Shares of Amazon rose more than 8 percent in after-hours trading, when the earnings were released. They had gained 3.8 percent, or $2.57, to $70.54, in regular trading.

The results surpassed analysts’ forecasts of 26 cents a share on $3.96 billion in revenue, according to a survey by Thomson Financial.

Looking ahead, the company said it now expects sales of as much as $4.43 billion in the current quarter, or 36 percent higher than a year ago. For the full year, Amazon forecast sales of up to $20.1 billion.

Gross margin declined slightly to 23.8 percent from 24.3 percent, mainly because Amazon lowered prices on some items, said Tom Szkutak, Amazon’s chief finance officer.

North America sales, including Amazon’s American and Canadian sites, were up 35 percent from a year ago, to $2.17 billion, while international sales were up 47 percent, to $1.89 billion. But adjusting for the effect of exchange rates, international sales grew 34 percent.

“We don’t think we are a good barometer for the economy,” Mr. Szkutak said.

Amazon, which is based in Seattle, has been making considerable enhancements to its offerings in recent months, in search of new revenue opportunities. In April, it announced a new service, called TextBuyIt, that allows customers to shop for products via text messaging on their cellphones. Earlier, the company lowered the price of its Kindle electronic reading device by $40, to $359, hoping to bolster sales.