According to CNBC, the company's chief financial officer Brian Olsavsky attributes the increase to the service's rising costs, releasing the following statement:
"The value of Prime to customers has never been greater. And the cost is also high, as we pointed out especially with shipping options and digital benefits, we continue to see rises in costs. So effective May 11, we're going to increase the price of our U.S. annual plan from $99 to $119 for new members. The new price will apply to renewals starting on June 16. Prime provides a unique combination of benefits, and we continue to invest in making this Prime program even more valuable for our members. As a reminder, we haven't increased the U.S. annual price Prime since our single increase, which was in March of 2014."