The authors model the fair Value of average rate financial options as
the solution of partial differential equations. When the average is sa
mpled discretely the equation to be solved is the Black-Scholes equati
on with the measure of the average-to-date being a parameter in the pr
oblem and a jump condition across sampling dates. The authors show how
to derive explicit results for the value of average rate options when
the average is measured arithmetically. When the average is measured
geometrically the problem must be solved numerically.