This　work　proposes　a　novel　approach　utilizing　an　oil-resistant,　thermally　stable　self-generating　foam　system　to　achieve　boundary　lubrication　drag　reduction　in　thermal　heavy　oil　transportation,　focusing　on　the　drag　reduction　characteristics　of　non-Newtonian　self-generating　foam　and　Newtonian　oil　phases　under　horizontal　pipe　co-flow　conditions.　Experiments　were　conducted　in　a　12-m-long,　25-mm-inner-diameter　horizontal　borosilicate　glass　pipe　with　roughened　walls,　measuring　pressure　gradients　for　co-flowing　high-viscosity　oil　and　foam　at　superficial　velocities　of　0.12–0.65　m/s　(oil)　and　0.06–0.63　m/s　(foam).　High-speed　imaging　identified　stratified　flow　(ST)　and　eccentric　core　annular　flow　(ECAF)　as　dominant　regimes　across　tested　conditions.　A　three-zone　two-phase　model　was　developed　for　horizontal　foam-oil　flows,　integrating　the　Carreau-Yasuda　rheology　of　self-generated　foam　at　60°C.　The　model　demonstrates　strong　agreement　with　experimental　data　over　broad　operational　ranges,　confirming　that　full　oil　core　encapsulation　by　foam　determines　the　critical　foam　injection　volume　fraction　for　maximum　drag　reduction.　Additionally,　optimal　oil　transport　efficiency　was　linked　to　specific　oil　core-to-pipe　diameter　ratios.　©　2025　Elsevier　Ltd