Audience measurement and tracking firm comScore released its estimates for US retail e-commerce, which puts online retail spending at $37.5bn for the second quarter of 2011, up 14% compared to a year earlier.

The growth in online spending during the quarter was primarily led by a 16% increase in the number of buyers.

comScore reveals that consumers are continuing to shift to the online channel, representing almost $1 in every $10 of discretionary spending.

E-commerce’s benefits of convenience and lower prices continue to be the drivers of the shift, even as broader consumer demand remained weak.

ComScore also noted that the April-June quarter was the third consecutive quarter of double-digit sales growth.

The company noted that web-based retailers occupied a wider market share with 70% of all Internet users making at least one online purchase during the period.

The top-performing online product categories included consumer electronics, excluding PC peripherals, computer hardware, computer software, and event tickets.

Each of these categories grew at least 15% compared to the year-earlier period.

The top 25 online retailers accounted for 66.4% of online spending, down from 67.7% a year ago and down from a peak of 69.9% in Q3 2010, as small and mid-sized retailers continue to regain lost market share.