A hot-pressed CdSe planar magnetron target was dc and rf sputtered in Ar and Ar/O2 mixtures. In the Ar case, the deposition rate increased linearly with dc or rf average power P. When O2 was added, it was efficiently gettered until a critical flow rate f2D which increased linearly with P. For 0< f2< f2D, the deposition rate was given by (r−bf2/P)(P−P0) where r, b, and P were 0.011 μm min−1, 0.032 μm min−1 W−1 and 25 W; the value of f2D/P was 0.04 ml min−1 W−1. In this range, there was a continuous increase in the oxygen content of the film until an equivalent composition of CdSe0.8O4.5 was reached at f2D. For f2≳ f2D, there was no further change in either the deposition rate or film composition. The behavior of the discharge pressure and impedance also indicate that the equivalent oxygen-rich phase was formed on the target surface at f2D. The film compositions were determined from Rutherford Backscattering and O16(d,p)O17 reaction analysis. The resistivity of the films increased with f2/P from 100 Ω cm at f2 = 0 to greater than 106 Ω cm at f2/P = 0.01 ml min−1 W−1 and this was associated with a decrease of 1% in the value of the hexagonal lattice parameter of the CdSe wurtzite structure but an oxygen-rich amorphous phase must be present to account for the 25 at.% oxygen in the films. All the films deposited at f2/P≳0.02 ml min−1 W−1 were amorphous.