Description of airspace and sectors

The Gander and Shanwick OCC are each responsible for half of the north Atlantic HLA airspace (border is at 30W°).
Both OCAs have been divided into various sectors to optimise traffic management and controller workload.
Sector Frequency Identifier Code
Gander Oceanic clearance 128.450 / 135.450 CZQX_OC_CTR OC
Gander FSS (southern tracks) 122.370 (12237.0 kHz) CZQX_S_CTR FSS-S
Gander FSS (northern tracks) 126.900 (12690.0 kHz) CZQX_N_CTR FSS-N
Gander FSS (west airspace) 127.100 (12710.0 kHz) CZQX_W_CTR FSS-W
Shanwick Oceanic clearance 127.650 / 123.950 EGGX_OC_CTR OCD
Shanwick FSS (southern tracks) 124.175 (12417.5 kHz) EGGX_S_CTR ORS
Shanwick FSS (northern tracks) 120.350 (12035.0 kHz) EGGX_N_CTR ORN
Shanwick/Gander FSS (general position) 127.900 (12790.0 kHz) EGGX_SG_CTR ORS
The first position to be opened is always Shanwick/Gander FSS (EGGX_SG_CTR), followed by Shanwick FSS (EGGX_S_CTR) or Gander FSS (CZQX_S_CTR).
Agree with EGGX_SG_CTR which position SG prefers. Prior permission required for Gander FSS (CZQX_W_CTR) by EGGX-Staff.

A diagram of the North Atlantic Airspace can be found here.