diff --git a/include/cantera/zeroD/ConstPressureReactor.h b/include/cantera/zeroD/ConstPressureReactor.h
index 103966f10..4e83d159f 100644
--- a/include/cantera/zeroD/ConstPressureReactor.h
+++ b/include/cantera/zeroD/ConstPressureReactor.h
@@ -55,7 +55,7 @@ public:
 
     virtual void updateState(doublereal* y);
 
-    virtual size_t componentIndex(std::string nm) const;
+    virtual size_t componentIndex(const std::string& nm) const;
 
 protected:
 
diff --git a/include/cantera/zeroD/FlowReactor.h b/include/cantera/zeroD/FlowReactor.h
index bc619c51e..a18ce489c 100644
--- a/include/cantera/zeroD/FlowReactor.h
+++ b/include/cantera/zeroD/FlowReactor.h
@@ -69,7 +69,7 @@ public:
     double distance() const {
         return m_dist;
     }
-    virtual size_t componentIndex(std::string nm) const;
+    virtual size_t componentIndex(const std::string& nm) const;
 
 protected:
 
diff --git a/include/cantera/zeroD/Reactor.h b/include/cantera/zeroD/Reactor.h
index 01c2c0649..3f7924c67 100644
--- a/include/cantera/zeroD/Reactor.h
+++ b/include/cantera/zeroD/Reactor.h
@@ -127,8 +127,7 @@ public:
         return m_pname[p];
     }
 
-    //        virtual std::string component(int k) const;
-    virtual size_t componentIndex(std::string nm) const;
+    virtual size_t componentIndex(const std::string& nm) const;
 
 protected:
     //! Pointer to the homogeneous Kinetics object that handles the reactions
diff --git a/include/cantera/zeroD/ReactorBase.h b/include/cantera/zeroD/ReactorBase.h
index af8ba8cdf..3dd9b1a88 100644
--- a/include/cantera/zeroD/ReactorBase.h
+++ b/include/cantera/zeroD/ReactorBase.h
@@ -30,7 +30,7 @@ class ReactorBase
 
 public:
 
-    ReactorBase(std::string name = "(none)");
+    explicit ReactorBase(const std::string& name = "(none)");
     virtual ~ReactorBase() {}
 
     //-----------------------------------------------------
@@ -41,7 +41,7 @@ public:
     std::string name() const {
         return m_name;
     }
-    void setName(std::string name) {
+    void setName(const std::string& name) {
         m_name = name;
     }
 
@@ -157,7 +157,7 @@ public:
 
     //@}
 
-    int error(std::string msg) const {
+    int error(const std::string& msg) const {
         writelog("Error: "+msg);
         return 1;
     }
@@ -185,7 +185,7 @@ protected:
 
 private:
 
-    void tilt(std::string method="") const {
+    void tilt(const std::string& method="") const {
         throw CanteraError("ReactorBase::"+method,
                            "ReactorBase method called!");
     }
diff --git a/include/cantera/zeroD/ReactorNet.h b/include/cantera/zeroD/ReactorNet.h
index c849deaaa..dc70c4f15 100644
--- a/include/cantera/zeroD/ReactorNet.h
+++ b/include/cantera/zeroD/ReactorNet.h
@@ -113,7 +113,7 @@ public:
         return m_integ->sensitivity(k, p)/m_integ->solution(k);
     }
 
-    double sensitivity(std::string species, size_t p, int reactor=0) {
+    double sensitivity(const std::string& species, size_t p, int reactor=0) {
         size_t k = globalComponentIndex(species, reactor);
         return sensitivity(k, p);
     }
@@ -135,7 +135,7 @@ public:
         return m_ntotpar;
     }
 
-    size_t globalComponentIndex(std::string species, size_t reactor=0);
+    size_t globalComponentIndex(const std::string& species, size_t reactor=0);
 
     void connect(size_t i, size_t j) {
         m_connect[j*m_nr + i] = 1;
diff --git a/src/zeroD/ConstPressureReactor.cpp b/src/zeroD/ConstPressureReactor.cpp
index 20f793c35..11cf89750 100644
--- a/src/zeroD/ConstPressureReactor.cpp
+++ b/src/zeroD/ConstPressureReactor.cpp
@@ -276,7 +276,7 @@ void ConstPressureReactor::evalEqs(doublereal time, doublereal* y,
     }
 }
 
-size_t ConstPressureReactor::componentIndex(string nm) const
+size_t ConstPressureReactor::componentIndex(const string& nm) const
 {
     if (nm == "H") {
         return 0;
diff --git a/src/zeroD/FlowReactor.cpp b/src/zeroD/FlowReactor.cpp
index 9c55231bc..4653ba433 100644
--- a/src/zeroD/FlowReactor.cpp
+++ b/src/zeroD/FlowReactor.cpp
@@ -125,7 +125,7 @@ void FlowReactor::evalEqs(doublereal time, doublereal* y,
 }
 
 
-size_t FlowReactor::componentIndex(string nm) const
+size_t FlowReactor::componentIndex(const string& nm) const
 {
     if (nm == "X") {
         return 0;
diff --git a/src/zeroD/Reactor.cpp b/src/zeroD/Reactor.cpp
index 69c065253..55e1036f2 100644
--- a/src/zeroD/Reactor.cpp
+++ b/src/zeroD/Reactor.cpp
@@ -318,7 +318,7 @@ void Reactor::addSensitivityReaction(size_t rxn)
 }
 
 
-size_t Reactor::componentIndex(string nm) const
+size_t Reactor::componentIndex(const string& nm) const
 {
     if (nm == "U") {
         return 0;
diff --git a/src/zeroD/ReactorBase.cpp b/src/zeroD/ReactorBase.cpp
index 45afcf51f..881a36754 100644
--- a/src/zeroD/ReactorBase.cpp
+++ b/src/zeroD/ReactorBase.cpp
@@ -12,7 +12,7 @@ using namespace std;
 namespace Cantera
 {
 
-ReactorBase::ReactorBase(string name) : m_nsp(0),
+ReactorBase::ReactorBase(const string& name) : m_nsp(0),
     m_thermo(0),
     m_vol(1.0),
     m_vol0(1.0),
diff --git a/src/zeroD/ReactorNet.cpp b/src/zeroD/ReactorNet.cpp
index 5bdf19730..a54d2ca2a 100644
--- a/src/zeroD/ReactorNet.cpp
+++ b/src/zeroD/ReactorNet.cpp
@@ -268,7 +268,7 @@ void ReactorNet::getInitialConditions(doublereal t0,
     }
 }
 
-size_t ReactorNet::globalComponentIndex(string species, size_t reactor)
+size_t ReactorNet::globalComponentIndex(const string& species, size_t reactor)
 {
     size_t start = 0;
     size_t n;