Singularity theory, local bifurcation analysis and numerical simulations are combined to investigate the steady-state behavior of the nonadiabatic autothermal tubular reactor in which a first-order exothermic reaction occurs. The steady-state model of the reactor consists of three first-order nonlinear ordinary differential equations with unmixed boundary conditions and contains six dimensionless groups. It is found that this simple convection-reaction model can have an arbitrarily large number of steady states. In addition, when the residence time is varied, the different possible bifurcation diagrams that exist vary from all those that occur in the classical cooled CSTR model to those found in the classical nonadiabatic tubular reactor model. We use local bifurcation techniques to make these predictions and confirm them with numerical solution of the full model. Singularity theory is used to classify the different types of bifurcation diagrams for a case where there is a maximum of five steady states.