American Express, while charging no commission to convert their Traveler's Cheques, offered me 174 pesetas to the US dollar. On the Internet, there are numerous sites for currency conversion.
Some sites give the official interbank rate.
This is the rate that Visa uses to convert your purchases from the foreign currency to US dollars. On the same day I got 189 pesetas as the interbank rate. This is still better than the AMEX exchange rate. This is what I found to be true throughout Europe. Check this out.