The　problem　of　power　allocation　with　uncoordinated　cooperative　jamming　is　addressed　in　this　paper　to　enhance　the　physical　layer　security　of　the　single-input-single-output　wiretap　channel　with　single-antenna　jammers.　Differing　from　the　existing　works　concerning　the　secrecy　rate　maximization,　this　paper　studies　the　problem　of　minimizing　the　secrecy　outage　probability　with　fixed　secrecy　rate,　where　the　channel　state　information　concerning　the　eavesdropper　is　only　known　statistically.　This　problem　is　formulated　as　an　optimization　problem　of　power　allocation　for　the　jamming　signals.　We　prove　that　the　optimization　problem　is　convex　in　essence,　and　the　optimal　solution　is　thus　conveniently　obtained　by　using　the　methods　of　golden　section　search　and　bi-section　search.　Simulation　results　show　that　the　proposed　approach　is　very　efficient　and　can　significantly　enhance　the　physical　layer　security　by　reducing　the　secrecy　outage　probability.　©　2019　IEEE.