Here is a Pprune thread regarding this subject.
http://www.pprune.org/tech-log/28841...ency-fuel.html
As you can see there is an OpSpec deviation from the 10% rule and it's called B43 International Reserve Policy. If you Google this you can see several threads that talk to the subject.
The B43 reserve policy stipulates that:
Enroute reserves can be calculated only for portions of the route where the aircraft is in Class 2 airspace and is more than an hour away from Class 1 airspace along the route.
Enroute reserves can be calculated at 10%, 5% or 3% by agreement with the FAA and based on aircraft capabilities.
Destination reserves must be increased from 30 minutes to 45 minutes. The destination reserves are computed the same as domestic reserevs-at final segment fuel flow, as opposed to "hold" over most distant airport (destination or farthest alternate).