visa [s] or [z]?

I have to post an update: I've heard some Visa ads recently, and in these ones they uniformly used [z]. Maybe they changed their official pronunciation because they realized that [z] is more common.

I thought it was "z". You guys made me doubt my memory.

Of course, the fact to which I was alluding previously is that there is Visa, the credit card company, and there are visas which you have stamped in your passport. It's up to the Visa people how their name should officially be pronounced but the latter is a different story. The Cambridge Dictionary gives only /"vi:.z@/ as does the American Heritage Dictionary.

http://dictionary.cambridge.org/define.asp?dict=CALD&key=88422&ph=on

http://www.bartleby.com/61/85/V0118500.html

Visa is always a "z" for me, as is "lousy". Greasy is an "s" sound, however.

Is it translate [s] or translate [z]?
Is it chromosome [s] or chromosome [z]?