diff --git a/opm/simulators/linalg/bda/BdaBridge.cpp b/opm/simulators/linalg/bda/BdaBridge.cpp
index 46a23fdd2..d88cae9b0 100644
--- a/opm/simulators/linalg/bda/BdaBridge.cpp
+++ b/opm/simulators/linalg/bda/BdaBridge.cpp
@@ -128,7 +128,7 @@ int checkZeroDiagonal(BridgeMatrix& mat) {
     int numZeros = 0;
     const int dim = 3;                    // might be replaced with mat[0][0].N() or BridgeMatrix::block_type::size()
     const double zero_replace = 1e-15;
-    if (diag_indices.size() == 0) {
+    if (diag_indices.empty()) {
         int N = mat.N();
         diag_indices.reserve(N);
         for (typename BridgeMatrix::iterator r = mat.begin(); r != mat.end(); ++r) {
@@ -169,7 +169,7 @@ void getSparsityPattern(BridgeMatrix& mat, std::vector<int> &h_rows, std::vector
     int sum_nnzs = 0;
 
     // convert colIndices and rowPointers
-    if (h_rows.size() == 0) {
+    if (h_rows.empty()) {
         h_rows.emplace_back(0);
             for (typename BridgeMatrix::const_iterator r = mat.begin(); r != mat.end(); ++r) {
                 int size_row = 0;
diff --git a/opm/simulators/linalg/bda/Reorder.cpp b/opm/simulators/linalg/bda/Reorder.cpp
index 13af74656..1834540c8 100644
--- a/opm/simulators/linalg/bda/Reorder.cpp
+++ b/opm/simulators/linalg/bda/Reorder.cpp
@@ -270,7 +270,7 @@ void findLevelScheduling(int *CSRColIndices, int *CSRRowPointers, int *CSCRowInd
     std::vector <int> rowsToStart;
 
     // since emplace_back() is used to fill, the vector must be empty
-    assert(rowsPerColor.size() == 0);
+    assert(rowsPerColor.empty());
 
     // find starting rows: rows that are independent from all rows that come before them.
     for (thisRow = 0; thisRow < Nb; thisRow++) {
diff --git a/opm/simulators/linalg/bda/openclSolverBackend.cpp b/opm/simulators/linalg/bda/openclSolverBackend.cpp
index e71f5c9c1..9d9fda463 100644
--- a/opm/simulators/linalg/bda/openclSolverBackend.cpp
+++ b/opm/simulators/linalg/bda/openclSolverBackend.cpp
@@ -49,7 +49,7 @@ openclSolverBackend<block_size>::openclSolverBackend(int verbosity_, int maxit_,
     try {
         std::vector<cl::Platform> platforms;
         cl::Platform::get(&platforms);
-        if (platforms.size() == 0) {
+        if (platforms.empty()) {
             OPM_THROW(std::logic_error, "Error openclSolver is selected but no OpenCL platforms are found");
         }
         out << "Found " << platforms.size() << " OpenCL platforms" << "\n";
@@ -89,7 +89,7 @@ openclSolverBackend<block_size>::openclSolverBackend(int verbosity_, int maxit_,
 
         platforms[platformID].getDevices(CL_DEVICE_TYPE_ALL, &devices);
 
-        if (devices.size() == 0){
+        if (devices.empty()) {
             OPM_THROW(std::logic_error, "Error openclSolver is selected but no OpenCL devices are found");
         }
         out << "Found " << devices.size() << " OpenCL devices" << "\n";
diff --git a/opm/simulators/timestepping/AdaptiveSimulatorTimer.cpp b/opm/simulators/timestepping/AdaptiveSimulatorTimer.cpp
index 13e06ea5c..d16fcaef2 100644
--- a/opm/simulators/timestepping/AdaptiveSimulatorTimer.cpp
+++ b/opm/simulators/timestepping/AdaptiveSimulatorTimer.cpp
@@ -137,14 +137,14 @@ AdaptiveSimulatorTimer& AdaptiveSimulatorTimer::operator++ ()
     /// \brief return max step length used so far
     double AdaptiveSimulatorTimer::maxStepLength () const
     {
-        if( steps_.size() == 0 ) return 0.0;
+        if( steps_.empty() ) return 0.0;
         return *(std::max_element( steps_.begin(), steps_.end() ));
     }
 
     /// \brief return min step length used so far
     double AdaptiveSimulatorTimer::minStepLength () const
     {
-        if( steps_.size() == 0 ) return 0.0;
+        if( steps_.empty() ) return 0.0;
         return *(std::min_element( steps_.begin(), steps_.end() ));
     }
 
diff --git a/opm/simulators/wells/GasLiftStage2.cpp b/opm/simulators/wells/GasLiftStage2.cpp
index 6c7a147a4..78409fca9 100644
--- a/opm/simulators/wells/GasLiftStage2.cpp
+++ b/opm/simulators/wells/GasLiftStage2.cpp
@@ -705,11 +705,11 @@ GasLiftStage2::
 removeSurplusALQ_(const Group &group,
     std::vector<GradPair> &inc_grads, std::vector<GradPair> &dec_grads)
 {
-    if (dec_grads.size() == 0) {
+    if (dec_grads.empty()) {
         displayDebugMessage2B_("no wells to remove ALQ from. Skipping");
         return;
     }
-    assert(dec_grads.size() > 0);
+    assert(!dec_grads.empty());
     const auto &gl_group = this->glo_.group(group.name());
     const auto &max_glift = gl_group.max_lift_gas();
     const auto controls = group.productionControls(this->summary_state_);
@@ -760,7 +760,7 @@ removeSurplusALQ_(const Group &group,
             // NOTE: recalculateGradientAndUpdateData_() will remove the current gradient
             //   from dec_grads if it cannot calculate a new decremental gradient.
             //   This will invalidate dec_grad_itr and well_name
-            if (dec_grads.size() == 0) stop_iteration = true;
+            if (dec_grads.empty()) stop_iteration = true;
             ++state.it;
         }
         else {
@@ -907,7 +907,7 @@ std::pair<std::optional<GasLiftStage2::GradPairItr>,
 GasLiftStage2::OptimizeState::
 getEcoGradients(std::vector<GradPair> &inc_grads, std::vector<GradPair> &dec_grads)
 {
-    if (inc_grads.size() > 0 && dec_grads.size() > 0) {
+    if (!inc_grads.empty() && !dec_grads.empty()) {
         this->parent.sortGradients_(inc_grads);
         this->parent.sortGradients_(dec_grads);
         // The largest incremental gradient is the last element
diff --git a/opm/simulators/wells/StandardWellEval.cpp b/opm/simulators/wells/StandardWellEval.cpp
index 02ec45659..a7ac494ce 100644
--- a/opm/simulators/wells/StandardWellEval.cpp
+++ b/opm/simulators/wells/StandardWellEval.cpp
@@ -716,14 +716,14 @@ template<class FluidSystem, class Indices, class Scalar>
 void
 StandardWellEval<FluidSystem,Indices,Scalar>::
 updatePrimaryVariablesNewton(const BVectorWell& dwells,
-                             const double dFLimit,
+                             [[maybe_unused]] const double dFLimit,
                              const double dBHPLimit) const
 {
     const std::vector<double> old_primary_variables = primary_variables_;
 
     // for injectors, very typical one of the fractions will be one, and it is easy to get zero value
     // fractions. not sure what is the best way to handle it yet, so we just use 1.0 here
-    const double relaxation_factor_fractions =
+    [[maybe_unused]] const double relaxation_factor_fractions =
         (baseif_.isProducer()) ? relaxationFactorFractionsProducer(old_primary_variables, dwells)
                                : 1.0;
 
diff --git a/opm/simulators/wells/WellState.cpp b/opm/simulators/wells/WellState.cpp
index 90b31b35a..97861d957 100644
--- a/opm/simulators/wells/WellState.cpp
+++ b/opm/simulators/wells/WellState.cpp
@@ -64,7 +64,7 @@ void WellState::base_init(const std::vector<double>& cellPressures,
             // Setup wellname -> well index mapping.
             const int num_perf_this_well = well_perf_data[w].size();
             std::string name = well.name();
-            assert( name.size() > 0 );
+            assert( !name.empty() );
             mapentry_t& wellMapEntry = wellMap_[name];
             wellMapEntry[ 0 ] = w;
             wellMapEntry[ 1 ] = connpos;