Online marketplaces, in particular Alibaba and Amazon, are proving central to the future of B2B commerce. But with each dominant in their own back yards, it will be when they go head-to-head in new markets that things really get interesting.By 2020, global online business-to-business retail sales will be more than double that of consumer retail, according to growth experts Frost & Sullivan, accounting for $6.7tn of revenue. At the heart of this surge to online purchasing are marketplaces, such as Amazon and Alibaba, which are creating a new era of many-to-many shopping opportunities for the B2B market.Many of the trends propelling consumer retail online are starting to impact the purchase journeys of business buyers, too. Why shouldn’t a shop owner running low on stock be able to re-order from the shop floor on their mobile phone and get the stock the next day?Andy Hoar, principal analyst at Forrester, specialising in e-business and channel strategy, says: “All B2B buyers are also B2C consumers, and they have a certain expectation. Amazon sets the standard for that.”The likes of Alibaba, Amazon and eBay have jumped in and filled a need, transferring the experience of consumer shopping to the context of B2B. Removing the complexity and creating choice for the buyer, as well as providing the opportunity to sell across new geographical borders, means many B2B sellers are now able to find new customers.Alibaba, which claimed the title of the biggest public offering in 2014, started its now wide-ranging online retail business as a B2B SME platform. In China, its consumer retail business now dwarfs its wholesale business. However, in the three months ending 31 December 2015, in terms of international sales, it did $97m in consumer sales and dwarfed that with its $221m in wholesale.One argument for the growth of the marketplaces is that they help make the B2B e-commerce experience more consumer-like, as well as simplifying otherwise time-consuming and expensive tasks.