Yes, but it more than the usual first class rate. Check here:

http://ircalc.usps.gov/

I suggest you Write “Air Mail” on it and use air mail rates.

Sorry Dear Heart, No one can really answer your question because things change over night. You’ll just have to contact the local Post Office in Spain. Here’s the crazy part… the new rule (whatever it is) could only be in effect for a short period then go back to the old way of doing things. I used to have a job that had the supervisors sitting in the middle of the room in a glass cage (with a door). High up over one of the corners of the cage were 3 different color lights that could be seen by all 500 (+) employee’s from any part of the large room. Just about every day one (or all) of the lights would start blinking which was a signal to us to put our call on hold and check the computer for some change somewhere in the world. It was a pain, but after a few years (like being a new parent) you get used to it. (smile). P.S. Maybe put those stamps in a safe dry storage area and save them for your Grandchildren. What would you think a stamp in good condition from say 1915 would be worth today? I’ll bet a lot more than you’ve paid so far !!

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I know for sure. You can not use USA stamps for a postcard send from Spain, or any country outside the USA. You need to buy stamps in the country you want to send from. USA international stamps are to send mail from the USA to other parts of the world, but nothing else.