Methods, apparatus, and products for determining thermal characteristics of instruction sets comprising one or more computer program instructions executed by a computer processor are disclosed that include tracking, in a performance counter, a number of classes of instructions run during execution of a plurality of instruction sets; identifying, for each instruction set, from the performance counter, a number of each class of instructions run during execution of the instruction set; and ranking the instruction sets in dependence upon the number of each class of instructions run during execution of each instruction set and a profile of thermal characteristics of classes of instructions.