Why are American-style options worth more than European-style options?
OK, my fault for not doing more research. Wikipedia explains this well: http://en.wikipedia.org/wiki/Option_style#Difference_in_value Basically, there are some cases where it's advantageous to exercise an American option early.  For non-gold currency options, this is only when the carrying cost (interest rate differential aka swap rate or rollover rate) is high. The slight probability that this may occur makes an American option worth slightly more.