After a bevy of reviews earlier in the week, Microsoft's Surface Pro running Windows 8 went on sale on Saturday in the United States and Canada. The 64GB model starts at $899, with the 128GB model reaching $999. 

A few hours after launch in retail stores and online, the 128GB version of the Surface Pro's demand looks to be high, selling out at the Microsoft Store, Staples, and Best Buy stateside. It's a similar situation in Canada.

Microsoft confirmed the news in a blog post, saying: "Customer response to the launch of Surface Pro has been amazing. We’re working with our retail partners who are currently out of stock of the 128GB Surface Pro to replenish supplies as quickly as possible. Our priority is to ensure that every customer gets their new Surface Pro as soon as possible." 

While sales numbers for the Surface RT haven't been disclosed, at the current rate we may be seeing higher demand for the Surface Pro. Of course there is the possibility stores weren't provided a tonne of stock, making for a quick sell-out. 

Read: Microsoft Surface RT shipments reached 900,000 in Q4?

The Pro offers a full version of Windows 8, higher storage and specs, thus the bigger price tag. Early reviews were somewhat positive for the ultrabook/tablet competitor, but noted 5 hour battery life being an issue. 

Later on Saturday, Windows Super Site first spotted that Microsoft's online store was also indicating the 64GB model as out of stock, but no official word has been provided by Microsoft.

Microsoft hasn't detailed further launch areas for the Surface Pro outside the US and Canada, but the Surface RT will be expanding its reach worldwide on 14 February to 13 more countries: Austria, Belgium, Denmark, Finland, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden and Switzerland.

Microsoft's Surface Pro launch event was cancelled because of the blizzard Nemo hitting New York City.

Will you be picking up a Surface Pro?