  We have used the Novikov-Thorne thin disk model to fit the continuum X-ray
spectra of three transient black hole X-ray binaries in the thermal state. From
the fits we estimate the dimensionless spin parameters of the black holes to
be: 4U 1543-47, a* = a/M = 0.7-0.85; GRO J1655-40, a* = 0.65-0.8; GRS 1915+105,
a* = 0.98-1. We plan to expand the sample of spin estimates to about a dozen
over the next several years. Some unresolved theoretical issues are briefly
discussed.
