diff --git a/include/cantera/base/XML_Writer.h b/include/cantera/base/XML_Writer.h
index f9eb1bebb..4d65f061a 100644
--- a/include/cantera/base/XML_Writer.h
+++ b/include/cantera/base/XML_Writer.h
@@ -85,22 +85,22 @@ public:
 
     template<class iter>
     void XML_writeVector(std::ostream& s, const std::string& indent,
-                         const std::string& name, int vsize, iter v) {
+                         const std::string& name, size_t vsize, iter v) {
         int ni;
         for (ni = 0; ni < _level; ni++) {
             s << _indent;
         }
         s << "<" << XML_filter(name) << "> ";
 
-        int n = vsize;
-        int n5 = n/5;
-        int i, j, k = 0;
+        size_t n = vsize;
+        size_t n5 = n/5;
+        size_t i, j, k = 0;
         for (j = 0; j < n5; j++) {
             for (i = 0; i < 5; i++) {
-                s << v[k] << (k < n - 1 ? ", " : "");
+                s << v[k] << (k+1 < n ? ", " : "");
                 k++;
             }
-            if (j < n5-1) {
+            if (j+1 < n5) {
                 s << std::endl;
                 for (ni = 0; ni < _level; ni++) {
                     s << _indent;
@@ -108,7 +108,7 @@ public:
             }
         }
         for (i = k; i < n; i++) {
-            s << v[k] << (k < n - 1 ? ", " : "");
+            s << v[k] << (k+1 < n ? ", " : "");
             k++;
         }
 
diff --git a/include/cantera/base/global.h b/include/cantera/base/global.h
index 8c5de92ef..584e72380 100644
--- a/include/cantera/base/global.h
+++ b/include/cantera/base/global.h
@@ -171,7 +171,7 @@ void writelogf(const char* fmt,...);
 //! Write an end of line character to the screen and flush output
 void writelogendl();
 
-void writeline(char repeat, int count,
+void writeline(char repeat, size_t count,
                bool endl_after=true, bool endl_before=false);
 
 //! @copydoc Application::Messages::logerror
diff --git a/include/cantera/equil/vcs_solve.h b/include/cantera/equil/vcs_solve.h
index 1a57848cb..62f4c22f1 100644
--- a/include/cantera/equil/vcs_solve.h
+++ b/include/cantera/equil/vcs_solve.h
@@ -1366,7 +1366,7 @@ private:
     void prneav() const;
 #endif
 
-    void checkDelta1(double* const ds, double* const delTPhMoles, int kspec);
+    void checkDelta1(double* const ds, double* const delTPhMoles, size_t kspec);
 
     //! Estimate equilibrium compositions
     /*!
diff --git a/src/base/global.cpp b/src/base/global.cpp
index 6d2ef2cfd..0d11bee13 100644
--- a/src/base/global.cpp
+++ b/src/base/global.cpp
@@ -68,7 +68,7 @@ void writelogendl()
     app()->writelogendl();
 }
 
-void writeline(char repeat, int count, bool endl_after, bool endl_before)
+void writeline(char repeat, size_t count, bool endl_after, bool endl_before)
 {
     if (endl_before) {
         writelogendl();
diff --git a/src/equil/BasisOptimize.cpp b/src/equil/BasisOptimize.cpp
index 694417994..273f4c2a6 100644
--- a/src/equil/BasisOptimize.cpp
+++ b/src/equil/BasisOptimize.cpp
@@ -404,7 +404,7 @@ static void print_stringTrunc(const char* str, int space, int alignment)
  ***********************************************************************/
 {
     int i, ls=0, rs=0;
-    int len = strlen(str);
+    int len = static_cast<int>(strlen(str));
     if ((len) >= space) {
         for (i = 0; i < space; i++) {
             writelogf("%c", str[i]);
diff --git a/src/equil/ChemEquil.cpp b/src/equil/ChemEquil.cpp
index bf3717dfc..b917d0555 100644
--- a/src/equil/ChemEquil.cpp
+++ b/src/equil/ChemEquil.cpp
@@ -292,7 +292,7 @@ int ChemEquil::estimateElementPotentials(thermo_t& s, vector_fp& lambda_RT,
 
     if (DEBUG_MODE_ENABLED && ChemEquil_print_lvl > 0) {
         for (size_t m = 0; m < m_nComponents; m++) {
-            int isp = m_component[m];
+            int isp = static_cast<int>(m_component[m]);
             string nnn = s.speciesName(isp);
             writelogf("isp = %d, %s\n", isp, nnn.c_str());
         }
@@ -329,7 +329,7 @@ int ChemEquil::estimateElementPotentials(thermo_t& s, vector_fp& lambda_RT,
     if (DEBUG_MODE_ENABLED && ChemEquil_print_lvl > 0) {
         writelog(" id      CompSpecies      ChemPot       EstChemPot       Diff\n");
         for (size_t m = 0; m < m_nComponents; m++) {
-            int isp = m_component[m];
+            size_t isp = m_component[m];
             double tmp = 0.0;
             string sname = s.speciesName(isp);
             for (size_t n = 0; n < m_mm; n++) {
@@ -1567,8 +1567,8 @@ void ChemEquil::adjustEloc(thermo_t& s, vector_fp& elMolesGoal)
     s.getMoleFractions(DATA_PTR(m_molefractions));
     size_t k;
 
-    int maxPosEloc = -1;
-    int maxNegEloc = -1;
+    size_t maxPosEloc = npos;
+    size_t maxNegEloc = npos;
     double maxPosVal = -1.0;
     double maxNegVal = -1.0;
     if (DEBUG_MODE_ENABLED && ChemEquil_print_lvl > 0) {
diff --git a/src/equil/vcs_setMolesLinProg.cpp b/src/equil/vcs_setMolesLinProg.cpp
index 39cbb99a0..dd95b5afb 100644
--- a/src/equil/vcs_setMolesLinProg.cpp
+++ b/src/equil/vcs_setMolesLinProg.cpp
@@ -21,12 +21,11 @@ static void printProgress(const vector<string> &spName,
                           const vector<double> &soln,
                           const vector<double> &ff)
 {
-    int nsp = soln.size();
     double sum = 0.0;
     plogf(" --- Summary of current progress:\n");
     plogf(" ---                   Name           Moles  -       SSGibbs \n");
     plogf(" -------------------------------------------------------------------------------------\n");
-    for (int k = 0; k < nsp; k++) {
+    for (size_t k = 0; k < soln.size(); k++) {
         plogf(" ---      %20s %12.4g  - %12.4g\n", spName[k].c_str(), soln[k], ff[k]);
         sum += soln[k] * ff[k];
     }
diff --git a/src/equil/vcs_solve_TP.cpp b/src/equil/vcs_solve_TP.cpp
index 9f36f08ed..1ab1711d8 100644
--- a/src/equil/vcs_solve_TP.cpp
+++ b/src/equil/vcs_solve_TP.cpp
@@ -36,12 +36,12 @@ static int  prnfm(void);
 /*****************************************************************************/
 
 void VCS_SOLVE::checkDelta1(double* const dsLocal,
-                            double* const delTPhMoles, int kspec)
+                            double* const delTPhMoles, size_t kspec)
 {
     std::vector<double> dchange(m_numPhases, 0.0);
-    for (int k = 0; k < kspec; k++) {
+    for (size_t k = 0; k < kspec; k++) {
         if (m_speciesUnknownType[k] != VCS_SPECIES_TYPE_INTERFACIALVOLTAGE) {
-            int iph = m_phaseID[k];
+            size_t iph = m_phaseID[k];
             dchange[iph] += dsLocal[k];
         }
     }
@@ -115,7 +115,7 @@ int VCS_SOLVE::vcs_solve_TP(int print_lvl, int printDetails, int maxit)
 
     solveFail = false;
 
-    int ll; // only used in DEBUG_MODE
+    size_t ll; // only used in DEBUG_MODE
     /* ****************************************************** */
     /* **** Evaluate the elemental composition         ****** */
     /* ****************************************************** */
@@ -3167,8 +3167,8 @@ L_END_LOOP:
          *  to conserve elements
          */
         double sumMax = -1.0;
-        int iMax = -1;
-        int jMax = -1;
+        size_t iMax = npos;
+        size_t jMax = npos;
         for (size_t i = 0; i < m_numRxnTot; ++i) {
             k = m_indexRxnToSpecies[i];
             double sum;
diff --git a/src/equil/vcs_util.cpp b/src/equil/vcs_util.cpp
index 07b649ae9..f0ac93736 100644
--- a/src/equil/vcs_util.cpp
+++ b/src/equil/vcs_util.cpp
@@ -164,7 +164,6 @@ double vcsUtil_gasConstant(int mu_units)
 
 const char* vcs_speciesType_string(int speciesStatus, int length)
 {
-    const char* sss;
     switch (speciesStatus) {
     case VCS_SPECIES_COMPONENT:
         return "Component Species";
diff --git a/src/thermo/RedlichKisterVPSSTP.cpp b/src/thermo/RedlichKisterVPSSTP.cpp
index a0192af16..b571d9bbc 100644
--- a/src/thermo/RedlichKisterVPSSTP.cpp
+++ b/src/thermo/RedlichKisterVPSSTP.cpp
@@ -760,7 +760,6 @@ void RedlichKisterVPSSTP::readXMLBinarySpecies(XML_Node& xmLBinarySpecies)
 #ifdef DEBUG_MODE
 void RedlichKisterVPSSTP::Vint(double& VintOut, double& voltsOut)
 {
-    int iA, iB, m;
     doublereal XA, XB;
     doublereal T = temperature();
     doublereal RT = GasConstant * T;
@@ -769,8 +768,8 @@ void RedlichKisterVPSSTP::Vint(double& VintOut, double& voltsOut)
     lnActCoeff_Scaled_.assign(m_kk, 0.0);
 
     for (int i = 0; i <  numBinaryInteractions_; i++) {
-        iA =  m_pSpecies_A_ij[i];
-        iB =  m_pSpecies_B_ij[i];
+        size_t iA =  m_pSpecies_A_ij[i];
+        size_t iB =  m_pSpecies_B_ij[i];
         XA = moleFractions_[iA];
         XB = moleFractions_[iB];
         if (XA <= 1.0E-14) {
@@ -780,7 +779,7 @@ void RedlichKisterVPSSTP::Vint(double& VintOut, double& voltsOut)
             XA = 1.0 - 1.0E-14;
         }
 
-        int N = m_N_ij[i];
+        size_t N = m_N_ij[i];
         vector_fp& he_vec = m_HE_m_ij[i];
         vector_fp& se_vec = m_SE_m_ij[i];
         double fac = 2.0 * XA - 1.0;
@@ -790,7 +789,7 @@ void RedlichKisterVPSSTP::Vint(double& VintOut, double& voltsOut)
         double polykp1 = fac;
         double poly1mk = fac;
 
-        for (m = 0; m < N; m++) {
+        for (size_t m = 0; m < N; m++) {
             doublereal A_ge = he_vec[m] - T * se_vec[m];
             Volts += A_ge * (polykp1 - (2.0 * XA * m * (1.0-XA)) / poly1mk);
             polykp1 *= fac;