Amazon has just reported its earnings for the fourth quarter of 2013. According to The Verge, Amazon CFO Tom Szkutak mentioned that the company is considering a price increase for its Amazon Prime customers in the US. The decision hasn't been made, but high shipping costs could prompt a price increase of between $20 and $40 a year for the service.

Prime began life as a service that offered free two-day shipping on many items for a flat, $79-a-year fee. As Amazon has branched out into tablets and streaming media, perks like the Instant Video service and Kindle Owners' Lending Library have been added to sweeten the deal. The potential price increase would be the first since Prime was introduced in the US in 2005.

Amazon reported $239 million in net income on $25.59 billion in total revenue for the fourth quarter of 2013, lower than analysts had expected. The company's guidance for the first quarter of 2014 projects net income to be somewhere between a profit of $200 million and a loss of $200 million on total revenues of between $18.2 and $19.9 billion.