Hmm, outside of my expertise here but as I understand it these...

Hmm, outside of my expertise here but as I understand it these are zones deemed to have oil in sufficient quantities to be worthwhile extracting.
As an example, Gordon #226 had 30 confirmed zones with the presence of hydrocarbons but 'only' 18 of these were confirmed oil pay zones.

What this then means is that in this one well they will start at the bottom pay zone and pump oil from there until it runs dry/pumps at such a low rate that it is not worthwhile continuing. They will then move on up to the next pay zone and do the same thing - 17 more times! All this from the one well with a minor delay in between zones for workover. Overall likely to be very good from a cost/benefit analysis of a single well wouldn't you say?