  We construct the higher twist structure functions that describe inclusive b
hadron decays in regions of phase space where the hadronic decay products carry
high energy but have low invariant mass. We show that, for B meson decays,
there are four new non-vanishing matrix elements of non-local operators. We
show that to subleading twist these decays are parametrized in terms of four
functions. We compute the tree-level matching for a general heavy-to-light
current and apply it to B -> X_s gamma. Using a simple model for these
functions we estimate the subleading twist contributions to this decay.
