diff --git a/opm/simulators/flow/python/PyFluidState.hpp b/opm/simulators/flow/python/PyFluidState.hpp
index b76d859ff..6df866b42 100644
--- a/opm/simulators/flow/python/PyFluidState.hpp
+++ b/opm/simulators/flow/python/PyFluidState.hpp
@@ -48,13 +48,10 @@ namespace Opm::Pybind
         };
     public:
         PyFluidState(Simulator *ebos_simulator);
-        std::unique_ptr<double []> getFluidStateVariable(
-                                   const std::string &name, std::size_t *size ) const;
-        std::unique_ptr<int []> getPrimaryVarMeaning(
-                                   const std::string &variable, std::size_t *size) const;
+        std::vector<double> getFluidStateVariable(const std::string &name) const;
+        std::vector<int> getPrimaryVarMeaning(const std::string &variable) const;
         std::map<std::string, int> getPrimaryVarMeaningMap(const std::string &variable) const;
-        std::unique_ptr<double []> getPrimaryVariable(
-                                   const std::string &idx_name, std::size_t *size ) const;
+        std::vector<double> getPrimaryVariable(const std::string &idx_name) const;
         void setPrimaryVariable(const std::string &idx_name, const double *data, std::size_t size);
 
     private:
diff --git a/opm/simulators/flow/python/PyFluidState_impl.hpp b/opm/simulators/flow/python/PyFluidState_impl.hpp
index 94d328025..6079f798d 100644
--- a/opm/simulators/flow/python/PyFluidState_impl.hpp
+++ b/opm/simulators/flow/python/PyFluidState_impl.hpp
@@ -31,14 +31,14 @@ PyFluidState(Simulator* ebos_simulator) : ebos_simulator_(ebos_simulator)
 // ------------------------------------
 
 template <class TypeTag>
-std::unique_ptr<int []>
+std::vector<int>
 PyFluidState<TypeTag>::
-getPrimaryVarMeaning(const std::string &variable, std::size_t *size) const {
+getPrimaryVarMeaning(const std::string &variable) const {
     Model &model = this->ebos_simulator_->model();
     auto &sol = model.solution(/*timeIdx*/0);
-    *size = model.numGridDof();
-    auto array = std::make_unique<int []>(*size);
-    for (unsigned dof_idx = 0; dof_idx < *size; ++dof_idx) {
+    auto size = model.numGridDof();
+    std::vector<int> array(size);
+    for (unsigned dof_idx = 0; dof_idx < size; ++dof_idx) {
         auto primary_vars = sol[dof_idx];
         array[dof_idx] = getVariableMeaning_(primary_vars, variable);
     }
@@ -106,20 +106,20 @@ getPrimaryVarMeaningMap(const std::string &variable) const
    kr_g = Gas relperm,
  */
 template <class TypeTag>
-std::unique_ptr<double []>
+std::vector<double>
 PyFluidState<TypeTag>::
-getFluidStateVariable(const std::string &name, std::size_t *size ) const
+getFluidStateVariable(const std::string &name) const
 {
     using ElementIterator = typename GridView::template Codim<0>::Iterator;
     using Element = typename GridView::template Codim<0>::Entity;
 
     Model &model = this->ebos_simulator_->model();
-    *size = model.numGridDof();
+    auto size = model.numGridDof();
+    std::vector<double> array(size);
     const auto& grid_view = this->ebos_simulator_->vanguard().gridView();
     /* NOTE: grid_view.size(0) should give the same value as
      *  model.numGridDof()
      */
-    auto array = std::make_unique<double []>(*size);
     ElementContext elem_ctx(*this->ebos_simulator_);
     ElementIterator elem_itr = grid_view.template begin</*codim=*/0>();
     const ElementIterator& elem_end_itr = grid_view.template end</*codim=*/0>();
@@ -128,7 +128,7 @@ getFluidStateVariable(const std::string &name, std::size_t *size ) const
         const Element& elem = *elem_itr;
         elem_ctx.updatePrimaryStencil(elem);
         elem_ctx.updatePrimaryIntensiveQuantities(/*timeIdx=*/0);
-        for (unsigned dof_idx = 0;dof_idx < elem_ctx.numPrimaryDof(/*timeIdx=*/0); ++dof_idx) {
+        for (unsigned dof_idx = 0; dof_idx < elem_ctx.numPrimaryDof(/*timeIdx=*/0); ++dof_idx) {
             const auto& int_quants = elem_ctx.intensiveQuantities(dof_idx, /*timeIdx=*/0);
             const auto& fs = int_quants.fluidState();
             unsigned global_dof_idx = elem_ctx.globalSpaceIndex(dof_idx, /*timeIdx=*/0);
@@ -139,16 +139,16 @@ getFluidStateVariable(const std::string &name, std::size_t *size ) const
 }
 
 template <class TypeTag>
-std::unique_ptr<double []>
+std::vector<double>
 PyFluidState<TypeTag>::
-getPrimaryVariable(const std::string &idx_name, std::size_t *size ) const
+getPrimaryVariable(const std::string &idx_name) const
 {
     std::size_t primary_var_idx = getPrimaryVarIndex_(idx_name);
     Model &model = this->ebos_simulator_->model();
     auto &sol = model.solution(/*timeIdx*/0);
-    *size = model.numGridDof();
-    auto array = std::make_unique<double []>(*size);
-    for (unsigned dof_idx = 0; dof_idx < *size; ++dof_idx) {
+    auto size = model.numGridDof();
+    std::vector<double> array(size);
+    for (unsigned dof_idx = 0; dof_idx < size; ++dof_idx) {
         auto primary_vars = sol[dof_idx];
         array[dof_idx] = primary_vars[primary_var_idx];
     }
diff --git a/opm/simulators/flow/python/PyMaterialState.hpp b/opm/simulators/flow/python/PyMaterialState.hpp
index d1bf20ad3..86831d0a3 100644
--- a/opm/simulators/flow/python/PyMaterialState.hpp
+++ b/opm/simulators/flow/python/PyMaterialState.hpp
@@ -45,8 +45,8 @@ namespace Opm::Pybind
         PyMaterialState(Simulator *ebos_simulator)
             : ebos_simulator_(ebos_simulator) { }
 
-        std::unique_ptr<double []> getCellVolumes( std::size_t *size);
-        std::unique_ptr<double []> getPorosity( std::size_t *size);
+        std::vector<double> getCellVolumes();
+        std::vector<double> getPorosity();
         void setPorosity(const double *poro, std::size_t size);
     private:
         Simulator *ebos_simulator_;
diff --git a/opm/simulators/flow/python/PyMaterialState_impl.hpp b/opm/simulators/flow/python/PyMaterialState_impl.hpp
index e8d07be53..2181b49ef 100644
--- a/opm/simulators/flow/python/PyMaterialState_impl.hpp
+++ b/opm/simulators/flow/python/PyMaterialState_impl.hpp
@@ -22,29 +22,29 @@
 namespace Opm::Pybind {
 
 template <class TypeTag>
-std::unique_ptr<double []>
+std::vector<double>
 PyMaterialState<TypeTag>::
-getCellVolumes( std::size_t *size)
+getCellVolumes()
 {
     Model &model = this->ebos_simulator_->model();
-    *size = model.numGridDof();
-    auto array = std::make_unique<double []>(*size);
-    for (unsigned dof_idx = 0; dof_idx < *size; ++dof_idx) {
+    auto size = model.numGridDof();
+    std::vector<double> array(size);
+    for (unsigned dof_idx = 0; dof_idx < size; ++dof_idx) {
         array[dof_idx] = model.dofTotalVolume(dof_idx);
     }
     return array;
 }
 
 template <class TypeTag>
-std::unique_ptr<double []>
+std::vector<double>
 PyMaterialState<TypeTag>::
-getPorosity( std::size_t *size)
+getPorosity()
 {
     Problem &problem = this->ebos_simulator_->problem();
     Model &model = this->ebos_simulator_->model();
-    *size = model.numGridDof();
-    auto array = std::make_unique<double []>(*size);
-    for (unsigned dof_idx = 0; dof_idx < *size; ++dof_idx) {
+    auto size = model.numGridDof();
+    std::vector<double> array(size);
+    for (unsigned dof_idx = 0; dof_idx < size; ++dof_idx) {
         array[dof_idx] = problem.referencePorosity(dof_idx, /*timeIdx*/0);
     }
     return array;
diff --git a/python/simulators/PyBlackOilSimulator.cpp b/python/simulators/PyBlackOilSimulator.cpp
index b70b16dfc..afb7165fb 100644
--- a/python/simulators/PyBlackOilSimulator.cpp
+++ b/python/simulators/PyBlackOilSimulator.cpp
@@ -95,9 +95,8 @@ int PyBlackOilSimulator::currentStep()
 }
 
 py::array_t<double> PyBlackOilSimulator::getCellVolumes() {
-    std::size_t len;
-    auto array = getMaterialState().getCellVolumes(&len);
-    return py::array(len, array.get());
+    auto vector = getMaterialState().getCellVolumes();
+    return py::array(vector.size(), vector.data());
 }
 
 double PyBlackOilSimulator::getDT() {
@@ -106,36 +105,32 @@ double PyBlackOilSimulator::getDT() {
 
 py::array_t<double> PyBlackOilSimulator::getPorosity()
 {
-    std::size_t len;
-    auto array = getMaterialState().getPorosity(&len);
-    return py::array(len, array.get());
+    auto vector = getMaterialState().getPorosity();
+    return py::array(vector.size(), vector.data());
 }
 
 py::array_t<double>
 PyBlackOilSimulator::
 getFluidStateVariable(const std::string &name) const
 {
-    std::size_t len;
-    auto array = getFluidState().getFluidStateVariable(name, &len);
-    return py::array(len, array.get());
+    auto vector = getFluidState().getFluidStateVariable(name);
+    return py::array(vector.size(), vector.data());
 }
 
 py::array_t<double>
 PyBlackOilSimulator::
 getPrimaryVariable(const std::string &variable) const
 {
-    std::size_t len;
-    auto array = getFluidState().getPrimaryVariable(variable, &len);
-    return py::array(len, array.get());
+    auto vector = getFluidState().getPrimaryVariable(variable);
+    return py::array(vector.size(), vector.data());
 }
 
 py::array_t<int>
 PyBlackOilSimulator::
 getPrimaryVarMeaning(const std::string &variable) const
 {
-    std::size_t len;
-    auto array = getFluidState().getPrimaryVarMeaning(variable, &len);
-    return py::array(len, array.get());
+    auto vector = getFluidState().getPrimaryVarMeaning(variable);
+    return py::array(vector.size(), vector.data());
 }
 
 std::map<std::string, int>