A siphon-based algorithm for deadlock prevention of a type of Petri nets called (SPMR)-P-3, which is a subclass of S(3)PGR(2), is presented in this correspondence. The proposed method is an iterative approach by adding two kinds of control places called ordinary control (OC) places and, weighted control (WC) places to the original model to prevent siphons from being unmarked. An OC place with ordinary arcs, which optimally prevent a siphon from becoming unmarked, is employed whenever it is possible, and otherwise, the WC places that adopt a conservative policy of controlling the release of parts into the system are used. Furthermore, this algorithm is not only for the subclass Petri nets but also for (SPR)-P-3, (ESPR)-P-3, (SLSPR)-L-2, and S(3)PGR(2) nets. The authors prove the liveness and reversibility of the controlled net, and hence establish the correctness of the deadlock prevention policy. Finally, numerical experiments indicate that the proposed policy appears to be more permissive than closely related approaches in the literature.