Jun 8, 2015 · 1 minute

Amazon has partnered with Universal Pictures and Illumination Entertainment to include the eponymous characters from the upcoming "Minions" film on the outside of its cardboard shipping boxes.

The Wall Street Journal reports that Amazon won't disclose financial details of the deal, but it's a fair bet to assume that Universal and Illumination have paid for access to this prime real estate, which didn't previously feature marketing.

The deal was revealed shortly after Amazon announced that it would offer free shipping on small items even if the order doesn't meet a minimum cost and the consumer doesn't pay $99 every year for access to the Amazon Prime service.

And that's what makes the advertising gambit so interesting. If Amazon is making money through the deal -- and it would be strange for it to feature ads on its boxes if it weren't -- it could make free deliveries more sustainable.

Here's how the Journal explains the potential upside for Amazon:

That is what makes the Minions campaign so interesting, experts say—Amazon is leveraging its volume in an indirect, unconventional way to offset costs.

'The Amazon Prime box is a very recognizable box now. I think it’s a neat concept,' said Satish Jindel, president of SJ Consulting Group Inc., a parcel industry research firm. 'There is a possibility of making money through scale by doing things like this that haven’t been done…and then building the scale even more.' Nixing the shipping costs might also make customers more likely to order items from Amazon's website. It doesn't make sense to pay more than the cost of an item in shipping; offering free deliveries removes that barrier from sales.

It's a self-supporting model. People buy more items because shipping is free, or because Amazon is offering more variety, so companies are more willing to pay for their advertisements to appear on the never-ending stream of cardboard.

The only surprising aspect of this is that Amazon didn't think of it sooner.