Consumers spent $517.36 billion online with U.S. merchants in 2018, up 15% from $449.88 billion spent the year prior, according to a new Internet Retailer’s analysis of industry data. That’s a slight slowdown from 2017, when online sales grew 15.6% year over year, according to Commerce Department figures.

Total retail sales hit $3.628 trillion last year, up 3.9% year over year from $3.490 trillion, Internet Retailer’s analysis of the U.S. Commerce Department’s total retail sales figures shows. Ecommerce represented a growing share of the retail market in 2018, taking a 14.3% share of total retail sales last year, up from 12.9% in 2017 and 11.6% in 2016.

More significant is that ecommerce sales represented more than half, or 51.9%, of all retail sales growth. This is the largest share of growth for purchases made online since 2008, when ecommerce accounted for 63.8% of all sales growth.

Amazon alone accounts for 40% of U.S. online retail. Twelve retailers filed for bankruptcy in 2018, and at least 1,521 retail storefronts were closed as a result. There were 21 acquisitions in 2018 in which both companies were retailers. Fifty-nine top online marketplaces in the U.S. sold $330 billion in gross merchandise sales to U.S. consumers.