OAS Z spread

CFA Level II
#1

I understand the concepts behind OAS and Z spread.

OAS = Z spread - Option Cost.

However, OAS and Z spread is in %. Is option cost also in %?

Thanks,

#2

I thought the spread was always in basis points?

#3

Yes but what about option cost?

#4

Yes, the option cost is given in per cent or basis points of additional yield.