The class of nonlinear systems that can be put into nonlinear observer form (linear system with output injection) can be broadened if we employ the system immersion. We provide an immersion algorithm for SISO nonlinear systems with relative degree r. The proposed algorithm is an extension of the previous results and does not require the relative degree 1 assumption. In addition, it is seen that the immersion can always be computed via algebraic computations and simple integrations except in a very special case in which the relative degree equals the system dimension (in this case, only one first order differential equation appears in the algorithm). (c) 2005 Elsevier Ltd. All rights reserved.