B2B marketplaces are a big and growing industry, but when it comes to sales volume, three marketplaces stand out: Amazon Business, Alibaba and eBay.

Amazon Business already claims 6 million customers and $35 billion in annualized gross merchandise sales — and it launched just eight years ago. But market analysts figure it is far from reaching a sales plateau.

Colin Sebastian, an R.W. Baird & Co. investment analyst who has accurately forecasted Amazon Business’s sales growth in recent years, has projected $80 billion in gross sales, including many by third-party sellers, before the end of this decade.