The 16GB version of the Google Nexus 7 tablet has sold out. A Google spokesman told the press on Monday that the company "underestimated demand." While you can visit Google Play and purchase a $199 8GB version of the Nexus 7, if you try to buy the $249 16GB version, it's unavailable. All you can do is leave your email address and ask Google to let you know if and when one becomes available.

The 16GB Nexus 7 is also reportedly sold out in the UK. At this point, Google has not indicated exactly when the Nexus 7 tablet will be available. The unexpectedly hot-selling tablet caught the industry by surprise just as it caught Google flat-footed. Other, more expensive, 7-inch tablets are selling well, but have not sold at the rate of the Nexus 7. The tablets with the hottest sales, primarily the Amazon Kindle Fire, are in good supply because Amazon anticipated strong sales during the holiday season in 2011 and built up supply.

The less expensive 8GB version of the Nexus 7 is still available, partly because Google had anticipated strong sales, and partly because sales haven't been as strong for the smaller version. A number of so-far unsubstantiated rumors suggest that the problem with the 8GB Nexus 7 is that it's far less useful without a connection to the cloud since many of its applications are cloud-based, and the device is reportedly not particularly useful without a high-speed wireless connection.

The Nexus 7 tablet has been shipping for only a week, and was announced only a month ago. The Google-branded device is built by Asus, which is also gearing up to build a Windows 8 tablet based on the company's existing Windows 7 tablet line.

A Google spokesperson contacted by FierceMobileIT declined to comment on the record, but did say that the 16GB version of the Nexus 7 should be back in stock shortly. The spokesperson also declined to say how many of the 16GB Nexus 7 tablets had been sold to date. "We're not ready to talk numbers yet," the spokesperson said.