The term stationery in the U.S. includes both paper products and certain other office supplies. Stationery is a 'mass noun' But if you need pencils, staples, printer ink, etc., the common term is 'office supplies' because most of us think of stationery as paper products only.

I would stick with "office supplies." At least in the US, we only use "stationary" to refer to paper office supplies (notepads, small notebooks), but even then I rarely hear it used.

I believe that stationary only refers to paper products. Office supplies can be other things like tape, scissors, etc.

They are synonyms. "Office supplies" is much more common today in the United States. This is probably because it is the term used nowadays by the big stores that sell them. "Stationery" has a range of meanings. The original meaning was limited to writing paper and envelopes. When I was a kid, "stationery stores" were common, but they were fairly small in size. Even so, just as a "drugstore" sells many things besides drugs, a "stationery store" always sold many things besides stationery. Staples changed everything when they introduced chains of huge stores selling a wide range of office supplies including desks and chairs, and now "office supplies" is more common. By the way, you spelled "stationery" correctly, with an -ery. Note that it is a completely different word from "stationary" with an -ary, which means an adjective for something that doesn't move.

Hello Marco! The two terms are often used interchangeably to mean the same thing (in England, at least), as you will see on the Staples website (http://www.staples.co.uk/), the Ryman website (http://www.ryman.co.uk/) and the WH Smith website (https://www.whsmith.co.uk/). All of these are major UK retailers. Hope this helps :)