  There are no known exact formulas for the valuation of a number of exotic
options, and this is particularly true for options under discrete monitoring
and for American style options. Therefore, one usually recourses to a Monte
Carlo Simulation approach, amongst other numerical methods, to estimate the
value of these options. The problem which then arises with this method is one
of variance reduction. Control variates are often used, and we present some
results concerning these control variables, for the valuation of Asian and
lookback options. An inequality on functions of correlations useful for
comparing estimators in variance reduction procedures is also provided.
