Is Slop Mandatory?
 

Would appreciate it if anyone can clarify whether Strategic Lateral Offset Procedures (SLOP) on the North Atlantic are mandatory. The Atlantic chart instructions regarding SLOP imply that SLOP is required for aircraft capable of the offset, without actually stating it as fact. Also, what about route offsets for other oceanic regions? How about Africa and South America? Are offsets mandatory, encouraged, or optional? Or somewhere in between? Many thanks for any inputs.

North Atlantic Programme Control Office
 

Strictly speaking the guidance says 'may' fly on one of 3 positions on track or 1nm or 2nm right. The guidance states that one of these 3 positions should be flown on all flights not just when wake turbulence is a factor.
The source website of the North Atlantic Programme Control Office has all the details:
See Slop Document and accompanying video Slop Video