1. A method of operating a computer to facilitate a commercial transaction involving a plurality of negotiable trading parameters, including the following steps resulting from the execution of a computer program; accepting in respect of a first entity a desired trading profile including at least desired values or ranges of multiple of said trading parameters and information for establishing one or more functional relationships between variations in at least a key trading parameter and other of said trading parameters; establishing one or more mathematical relationships between variations in at least the key trading parameter and the other of said trading parameters; wherein said one or more mathematical relationships can be used to determine a set of trading profiles having substantially equal expected desirability values to said desired trading profile; and determining whether a submitted trading profile from a second entity has a desirability value that equals or exceeds the desirability value of said desired trading profile using said one or more mathematical relationships.