Walmart's biggest struggle against Amazon is exactly what you'd expect: online sales. Amazon accounts for about 40% of all online retail sales in the U.S. Walmart, despite being second on the list, only makes up about 5%. Part of the problem is Amazon's Prime subscription service which has created incredible consumer loyalty. But now, Walmart is reportedly ready to challenge Amazon with a new program called Walmart+. Walmart+ will likely be a relaunch of Walmart's $98 per year Delivery Unlimited, but with additional perks. What these perks will be, and what it will cost are still unspecified. But one thing is clear: Walmart will have to adjust to maintain its position as America's top-grossing retailer.