Apple's iPad is challenging Amazon's Kindle for the lead in the U.S. e-reader market, a retail research firm said today.

But while iPad ownership among readers of electronic books still lags behind the Kindle, users of Apple's tablet are more satisfied with their devices, said ChangeWave's director of research Paul Carton.

According to ChangeWave's survey earlier this month of more than 2,800 American consumers, 75 per cent of iPad owners said they were "very satisfied" with their tablets. Kindle owners, meanwhile, were less kind: Just 54 per cent answered the same when asked how they felt about Amazon's e-reader.

However, when the "somewhat satisfied" numbers are added to each device's total, the race is much tighter, with the iPad leading the Kindle by 96 per cent to 92 per cent.

The iPad may be more than three times pricier than the Kindle - Apple's least-expensive tablet costs $499 , while Amazon's current Kindle starts at $139 - the iPad has doubled its share of the e-reader market since August, said Carton, and is now within 15 percentage points of the Kindle.

"The Amazon Kindle is hanging on to a rapidly diminishing lead over the Apple iPad among current e-reader owners," said Carton in a research note published to the ChangeWave site Tuesday.

ChangeWave's November consumer survey pegged the iPad's share of the U.S. e-reader market at 32 per cent, up 16 percentage points since August, and put the Kindle at a 47 per cent share, down 15 points from August's 62 per cent.

Apple iPad

"The e-reader market has essentially become a two-horse race between the Kindle and the iPad," said Carton, who noted that the also-rans -- Sony's Reader and Barnes and Noble's Nook -- collectively accounted for only 9% of the market.

And Apple has the high ground in the next 90 days, Carton said as he pointed out other survey results.

Of those consumers who said that they plan to buy an e-reader in the next three months, 42 per cent told ChangeWave that they would purchase an iPad . One-in-three, or 33 per cent, picked the Kindle.

"The iPad will be the biggest beneficiary of the expanding e-reader market this holiday season," said Carton.

The e-reader business is expected to expand even more in 2011, when some analysts believe prices for devices with black-and-white displays will drop to as low as $50 .