Increase in transmission symbol-rate as well as order of quadrature amplitude modulation (QAM) is identified as the most economical way to reduce cost per transmitted bit. In particular, next generation transponders aim at supporting datarates up to 1 Tb/s employing superchannels due to electrical components’ bandwidth limitations. Furthermore, the introduction of a flexible-grid architecture can maximize throughput by minimizing spectral gaps in available optical spectrum. Keeping in view these design options, we conducted several high capacity experiments with tier1 operator Orange using their field deployed standard single mode fiber (SSMF, G.652), having a total length of 762 km, connecting the cities Lyon and Marseille in France. In particular we employed four subcarriers per Tb/s superchannel, each modulated by PM-16QAM, PM-32QAM and PM-64QAM with per carrier symbol-rates of 41.2 GBd, 33 GBd and 34 GBd, respectively. The subcarrier spacing was 50 GHz for the PM- 16QAM case and 37.5 GHz for both the PM-32QAM and PM-64QAM cases allowing in total 241.0 Tb/s, 321.0 Tb/s and 321.2 Tb/s superchannels over C-band and resulting in potential C-band capacities of 24.0 Tb/s, 32.0 Tb/s and 38.4 Tb/s, respectively. After field transmission the maximum available OSNR0:1nm margin compared to the required OSNR0:1nm at forward error correction (FEC) threshold was 8.2 dB, 5.4 dB and 4.2 dB for PM-16QAM, PM-32QAM and PM-64QAM, respectively. The transmission reach for PM-16QAM and PM- 32QAM modulated superchannels was extended to 1571 km and 1065 km using erbium doped fiber amplified SSMF spans of 101 km length.