  The present paper solves the problem of the group classification of the
general Burgers' equation $u_t=f(x,u)u_x^2+g(x,u)u_{xx}$, where $f$ and $g$ are
arbitrary smooth functions of the variable $x$ and $u$, by using Lie method.
The paper is one of the few applications of an algebraic approach to the
problem of group classification: the method of preliminary group
classification. A number of new interesting nonlinear invariant models which
have nontrivial invariance algebras are obtained. The result of the work is a
wide class of equations summarized in table form.
