We describe the operation of a high average power, high‐repetition rate, femtosecond optical parametric oscillator in the important 3–5 μm spectral region. The Ti:sapphire pumped optical parametric oscillator was based on the nonlinear material potassium niobate. The idler wavelength was continuously tunable over the 2.3–5.2 μm region and average powers as high as 170 mW were measured. At 5.2 μm, average powers of more than 20 mW were recorded. Idler pulse durations were determined using cross‐correlation techniques and pulses as short as 60 fs were measured in the midinfrared.