Free Shipping From Wal-Mart

Wal-Mart is trying to get a jump on Amazon's second annual sales bonanza.

The world's largest retailer is offering a free 30-day trial on its two-day unlimited shipping service, and an extra month free for paying members, starting Wednesday as it looks to sharpen its attack against the online leader.

Beginning Friday, it will also offer discounts on an array of products from swimming pools to electronics that will ramp up as July goes by. These discounts, or what Wal-Mart calls "rollbacks," typically last 90 days or longer.

Wal-Mart's moves come as Amazon is expected to launch for the second year a sales bonanza called Prime Day, which it has touted as bigger than "Black Friday." It underscores how serious Wal-Mart is about boosting its online sales,