This paper addresses the specification of pressure and velocity boundary conditions for 2D and 3D lattice Boltzmann BGK models (LBGK). A novel method based on the bounceback of non-equilibrium distribution is proposed to specify these conditions, which are consistent with wall boundary conditions. When combined with an improved incompressible LBGK model, this method accurately simulates plane Poiseuille flow driven by pressure differences. The half-way wall bounceback boundary condition, known for its second-order accuracy in 2D Poiseuille flow with forcing, is used with the proposed pressure and velocity inlet/outlet conditions to study 2D Poiseuille flow and 3D square duct flow. Numerical results show approximately second-order accuracy, with errors comparable to those of other published boundary conditions. The half-way wall bounceback boundary condition is also noted for its superior stability compared to other boundary conditions. The paper recommends using the half-way wall bounceback boundary condition for stationary walls and the proposed boundary conditions for flow boundaries.This paper addresses the specification of pressure and velocity boundary conditions for 2D and 3D lattice Boltzmann BGK models (LBGK). A novel method based on the bounceback of non-equilibrium distribution is proposed to specify these conditions, which are consistent with wall boundary conditions. When combined with an improved incompressible LBGK model, this method accurately simulates plane Poiseuille flow driven by pressure differences. The half-way wall bounceback boundary condition, known for its second-order accuracy in 2D Poiseuille flow with forcing, is used with the proposed pressure and velocity inlet/outlet conditions to study 2D Poiseuille flow and 3D square duct flow. Numerical results show approximately second-order accuracy, with errors comparable to those of other published boundary conditions. The half-way wall bounceback boundary condition is also noted for its superior stability compared to other boundary conditions. The paper recommends using the half-way wall bounceback boundary condition for stationary walls and the proposed boundary conditions for flow boundaries.