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An electrically excited oxygen-iodine laser with a scaled-up electric discharge has been designed and operated. Singlet delta oxygen is generated in a capacitively coupled RF discharge sustained in the plenum of a M=3 nozzle. The discharge operates at pressures up to p0=120 torr, powers up to 4.5 kW, and flow rates up to 0.5 mole/sec of 0-15 % O2 in He. Singlet delta oxygen yields up to Y=7.5 % have been measured using absolute infrared emission spectroscopy. Small signal gain on the I*(2P1/2,F′=3)→I(2P3/2,F″=4) iodine atom transition in the supersonic flow has been measured by tunable diode laser absorption spectroscopy, up to γ=0.209 %/cm. The addition of NO to the laser mixture and injection of chilled helium to reduce the laser mixture temperature have been shown to enhance laser performance considerably. Other modifications, including the addition of argon to the laser mixture, chilling the main flow through the electric discharge, and dissociating iodine directly by electron impact in an auxiliary electric discharge have not resulted in further gain increase. Laser action has been achieved using a transverse resonator in the supersonic cavity, with laser output power up to PL=7.8 W.