Block 50/52 are the only versions with almost as many dual & single-seat airframes. Many are used for specialized missions like Wild Weasel and require a crew of two to handle the cockpit workload linked to the additional avionics (housed in dorsal spine)
The F-16A block 15
is the most numerous F-16 variant with 662 airframes originally built. It is closely followed by the F-16C block 40
(485 airframes) and the F-16C block 30
(479 airframes). For most variants, the single-seat variants (A and C models) far outweigh the dual-seat variants (B and D). For the A/B models and the early C/D models (up to block 40/42), the ratio is about 6 to 1 - 6 single-seaters are built for every two-seater. This is a normal ration for training purposes.
The most notable exception is the block 52
with about the same amount of C and D variants build. The reason for this is that many F-16D block 52
aircraft are used in a role with a missionized two-seater. This demanding mission role adds specialized equipment to the F-16 and the additional cockpit workload requires a crew of two - pilot plus WSO (Weapon Systems Officer). The same is true for the F-16E/F block 60