Thanks daddylonglegs.

Had experimented with lookup, but as you say: the data must be sorted and I cannot rely on other departments to adhere to this.

The lookup table is essentially a truth table that I need the array of values to be returned from - summing them is not useful, unfortunately - unless I misunderstand the functionality of SUMIF. (Summing a selection of data based on criteria being met...?)

Cheers, Jason.