2.5 Gbit/s NRZ transoceanic system aspects are simulated using a recirculating loop experiment. At 10 000 km, penalties of <1 dB are achieved and a wavelength window of 8 nm obtained. At transatlantic distances penalties of <1 dB are achieved for fibre dispersions to + 1 ps/nm/km. The robust nature of the saturated amplifier system is demonstrated when <3 dB penalty resulted from adding 450 dB loss to the system budget.