  We have measured the Hall-plateau width and the activation energy of the
bilayer quantum Hall (BLQH) states at the Landau-level filling factor $\nu=1$
and 2 by tilting the sample and simultaneously changing the electron density in
each quantum well. The phase transition between the commensurate and
incommensurate states are confirmed at $\nu =1$ and discovered at $\nu =2$. In
particular, three different $\nu =2$ BLQH states are identified; the compound
state, the coherent commensurate state, and the coherent incommensurate state.
