  We have used a detailed non-LTE radiative transfer code to model new APEX
CO(J=3-2) data, and existing CO radio line data, on a sample of 40 AGB S-stars.
The derived mass-loss-rate distribution has a median value of 2E-7 Msun/yr, and
resembles values obtained for similar samples of M-stars and carbon stars.
Possibly, there is a scarcity of high-mass-loss-rate (>=1E-5 Msun/yr) S-stars.
The distribution of envelope gas expansion velocities is similar to that of the
M-stars, the median is 7.5 km/s, while the carbon stars, in general, have
higher gas expansion velocities. The mass-loss rate correlates well with the
gas expansion velocity, in accordance with results for M-stars and carbon
stars.
