Around $13.7 billion was spent on online retail transactions in the 12 months to May 2013, according to the NAB Online Retail Sales Index.
This is equivalent to 6.1 per cent of bricks and mortar spending in the year to April 2013.
This compares to the equivalent of 5.7 per cent of traditional bricks and mortar retail sales for the 12 months to October 2012.
Online sales dropped slightly in May to 18 per cent year-on-year growth, compared to 24 per cent year-on-year growth in April.
However, it is stronger than February and March figures, according to the Index.
Bricks and mortar retail grew 3.2 per cent year-on-year in April, compared to 2.4 per cent year-on-year in March.
NAB said the growth trend for shopfront retail was 3 per cent year-on-year in April.
"While growth for online sales was a little softer in May, this may in part reflect a boost to sales in April, related to the Mother's Day 'Click Frenzy' promotion on April 23, which generated a strong sales lift for a number of participating brands," NAB said in its report.
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