Cyber Monday was the biggest online shopping day ever, according to Jay Henderson, strategy director at IBM Smarter Commerce, and mobile shopping played a significant role in its growth.

Spending increased 30.3% from the previous year, with mobile devices accounting for accounted for 12.9% of all sales. That's a 96% increase from 2011, according to IBM's Smarter Commerce initiative.

Mobile sales were lower on Cyber Monday than on Black Friday, however, a change that IBM attributes to more customers returning to work and shopping from their PCs. Both mobile traffic and mobile sales fell by 20% from Black Friday to Cyber Monday.

The iPad continues to be the top tablet in mobile commerce, accounting for 7.1% of all Cyber Monday traffic and 90.5% of all tablet-driven traffic. Second among tablets was Amazon's Kindle, at 2.6%. The Samsung Galaxy was next at 2%.

Mobile shoppers continue to prefer smartphones, however, as a slight majority (58.1%) used smartphones rather than tablets on the shopping "holiday."

Despite the overall spending increases, the average order size dipped 6.6% to $185.12, the report said. Social sales also decreased, as Facebook, Twitter, LinkedIn and YouTube generated just 0.41% of all online sales, a 26% drop from 2011.

The report was based on IBM's Digital Analytics Benchmark which tracks e-commerce data from 500 retailers nationwide on daily basis.