The Mark III design encompassed the greatest improvement in the technology since its commercialisation. The focus was to make the technology more robust and easier to use in operations. The total redesign of the downcomer assembly allowed it to be isolated and unblocked much more easily compared to the Mark II design. The Mark III design also saw slurry flow per downcomer to be increased from 60 m/h to 75–85 m/h using larger orifice sizes in the slurry lenses.
The Mark III Cell was introduced in 2000. It included the following improvements:
* a new slurry lens orifice design (see Figures 7 and 8)
* a new design downcomer and nozzle
* a new design flat plate bubble dispersers
* a stainless steel adjustable above and in-froth wash water system (see Figure 9)
* automated air and wash water flow control
* air-isolating slurry-eliminating valves ("AISE valves") 
* a bottom-fed new slurry distributor.
The earlier models of the Jameson Cell used orifice plates to generate the downcomer jet. The new slurry lens design had a smooth, shallow entry angle that created an optimum flow regime over the ceramic, reducing wear and extending its life. The shape resulted in a decrease in power consumption by the feed slurry pump by up to 10% and resulted in better jet formation that improved air entrainment.
For coal applications, the wash water addition system was changed from a tray to stainless-steel circular rings attached to a manual lifting system. This allowed the flexibility of an easy transition from above-froth wash water addition to the in-froth addition that might be necessary for high concentrate-grade operations. For metals applications, new design wash water trays consisting of removable rubber mats for easy maintenance were used. 
The AISE valves were developed to prevent solids being sucked back into the air lines when individual downcomers become blocked. Solids depositing in the air lines and their build up in the air distributor decreases flotation performance as it prevents air from being efficiently entrained in the downcomers.