. derivative instruments are used to mitigate the price risk between the time foreign and domestic crude oil and other feedstock purchases for refinery supply are priced and when they are actually refined into salable petroleum products . in addition , natural gas options are in place to manage the price risk associated with approximately 60% ( 60 % ) of the anticipated natural gas purchases for refinery use through the first quarter of 2004 and 50% ( 50 % ) through the second quarter of 2004