Shell Rotella Synthetic and Helix Ultra use the XHVI group III.
When oil is hydrocracked, long chain paraffin slack wax is cracked off. With hydrotreatment, they can break that long chain wax down into short chain hydrocarbons of roughly equal size with high purity and repeatability levels.
It's in many ways similar to a "labratory" synthetic but the source of the hydrocarbons is slack wax rather than natural gas.