As has been posted here RON values differ based on region. 87 US RON = 91 Europe RON. The conversion is explained here:
Octane rating conversions - PencilGeek's BMW Blog
Euro to US:
US (RON) = Euro RON *0.954
So if Euro RON rating is 91, the US RON equivalent is ~87
On a brighter note Total Parco's High-Super is supposed to be 90 RON which if put in the formula yields a US RON of ~86 RON.
Fuels - Total Parco Pakistan Ltd