We classify the spherical birational sheets in a complex simple simply-connected algebraic group. We use the classification to show that, when G is a connected reductive complex algebraic group with simply-connected derived subgroup, two conjugacy classes O1, O2 of G
Nearby in the stack
lie in the same birational sheet, up to a shift by a central element of
G
, if and only if the coordinate rings of
O1
and
O2
are isomorphic as
G
-modules. As a consequence, we prove a conjecture of Losev for the spherical subvariety of the Lie algebra of