Multicomponent sputtering is examined using as examples amorphous Gd−Co alloys and related ternary systems Gd−Co−Au and Gd−Co−Mo. Film composition was studied as a function of bias voltage, target voltage, pressure, system geometry and target composition. If the sputtering yield, ε, of one constituent is much greater than the yield of the other elements in the system, it is possible to express the film composition as a simple function of the above parameters. For example, in the Gd−Co system εGd ≳ εCo and the Co/Gd ratio in the film is given by (Co/Gd)film = (Co/Gd)target/1 − K (Vb/Vt), where Vb is the effective bias voltage, Vt is the target voltage, and K is a system constant which depends largely on the geometry. The equation involves a number of simplifying assumptions which are only valid in the low bias, low pressure regime. A more complex expression must be used outside of these limits. It has also been shown that there is a simple relationship between sputtering gas incorporation in the film and the effective bias voltage, which provides an independent check on the validity of the sputtering equation.