Heavy　oil　accounts　for　two-thirds　of　the　world　oil　resources　but　contributes　only　one-seventh　of　the　world　oil　production　due　to　its　high　oil　viscosity　and　heavy　distillates.　Steam　injection　has　been　widely　used　for　heavy　oil　recovery　by　heating　up　the　reservoir　to　reduce　oil　viscosity.　However,　severe　carbon　loss　to　coking　causes　low　recovery　efficiency　and　high　energy　consumption.　Here,　we　report　supercritical　water　injection　for　heavy　oil　recovery.　Supercritical　water　is　expected　to　be　both　a　heat　carrier　and　an　organic　solvent,　thereby　not　only　reducing　oil　viscosity　but　also　dissolving　heavy　distillates　to　avoid　coking.　To　test　its　feasibility,　core　experiments　were　first　conducted　to　simulate　the　recovery　process.　Results　showed　that　supercritical　water　flooding　improved　oil　recovery　by　17%　and　reduced　heat　consumption　by　34%　versus　classsical　steam　flooding.　Further,　to　clarify　its　recovery　mechanism,　a　visualization　technique　and　a　quantitative　method　were　developed　for　regulating　phase　behaviors　and　upgrading　reactions　between　heavy　oil　and　supercritical　water.　Results　showed　that　supercritical　water　has　good　miscibility　with　heavy　oil,　and　it　is　the　key　to　both　enhanced　oil　recovery　and　in　situ　upgrading.　High　miscibility　means　formation　of　supercritical　water　clusters　around　organic　macromolecules,　which　makes　asphaltene　difficult　to　aggregate　and　polymerize　to　form　coke　but　easy　to　decompose　to　form　maltene　and　recover.　Overall,　supercritical　water　injection　has　made　great　advances　in　enhanced　oil　recovery,　energy　saving,　and　in　situ　upgrading　for　heavy　oil　recovery.　The　work　provides　a　sound　basis　for　its　application　in　oilfields.