diff --git a/example/user_defined_eos.ipynb b/example/user_defined_eos.ipynb
index 71467ae..6feecc7 100644
--- a/example/user_defined_eos.ipynb
+++ b/example/user_defined_eos.ipynb
@@ -1240,9 +1240,9 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "feos",
+   "display_name": "Python 3 (ipykernel)",
    "language": "python",
-   "name": "feos"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
diff --git a/src/python/state.rs b/src/python/state.rs
index 8eed471..0db45cf 100644
--- a/src/python/state.rs
+++ b/src/python/state.rs
@@ -525,6 +525,29 @@ macro_rules! impl_state {
                 self.0.ln_phi().view().to_pyarray(py)
             }
 
+            /// Return logarithmic pure substance fugacity coefficient.
+            /// 
+            /// For each component, the hypothetical liquid fugacity coefficient
+            /// at mixture temperature and pressure is computed.
+            /// 
+            /// Returns
+            /// -------
+            /// numpy.ndarray
+            #[pyo3(text_signature = "($self)")]
+            fn ln_phi_pure<'py>(&self, py: Python<'py>) -> PyResult<&'py PyArray1<f64>> {
+                Ok(self.0.ln_phi_pure()?.view().to_pyarray(py))
+            }
+
+            /// Return logarithmic symmetric activity coefficient.
+            /// 
+            /// Returns
+            /// -------
+            /// numpy.ndarray
+            #[pyo3(text_signature = "($self)")]
+            fn ln_symmetric_activity_coefficient<'py>(&self, py: Python<'py>) -> PyResult<&'py PyArray1<f64>> {
+                Ok(self.0.ln_symmetric_activity_coefficient()?.view().to_pyarray(py))
+            }
+
             /// Return derivative of logarithmic fugacity coefficient w.r.t. temperature.
             ///
             /// Returns
diff --git a/src/state/properties.rs b/src/state/properties.rs
index b56cf73..5adffa2 100644
--- a/src/state/properties.rs
+++ b/src/state/properties.rs
@@ -2,11 +2,12 @@ use super::{Derivative::*, PartialDerivative, State};
 use crate::equation_of_state::{EntropyScaling, EquationOfState, MolarWeight};
 use crate::errors::EosResult;
 use crate::EosUnit;
-use ndarray::{Array1, Array2};
+use ndarray::{arr1, Array1, Array2};
 use num_dual::DualNum;
 use quantity::{QuantityArray, QuantityArray1, QuantityArray2, QuantityScalar};
 use std::iter::FromIterator;
 use std::ops::{Add, Sub};
+use std::rc::Rc;
 
 #[derive(Clone, Copy)]
 pub(crate) enum Evaluate {
@@ -300,6 +301,32 @@ impl<U: EosUnit, E: EquationOfState> State<U, E> {
             .unwrap()
     }
 
+    /// Logarithm of the fugacity coefficient of all components treated as pure substance at mixture temperature and pressure.
+    pub fn ln_phi_pure(&self) -> EosResult<Array1<f64>> {
+        let pressure = self.pressure(Contributions::Total);
+        (0..self.eos.components())
+            .map(|i| {
+                let eos = Rc::new(self.eos.subset(&[i]));
+                let state = Self::new_npt(
+                    &eos,
+                    self.temperature,
+                    pressure,
+                    &(arr1(&[1.0]) * U::reference_moles()),
+                    crate::DensityInitialization::Liquid,
+                )?;
+                Ok(state.ln_phi()[0])
+            })
+            .collect()
+    }
+
+    /// Activity coefficient $\ln \gamma_i = \ln \varphi_i(T, p, \mathbf{N}) - \ln \varphi_i(T, p)$
+    pub fn ln_symmetric_activity_coefficient(&self) -> EosResult<Array1<f64>> {
+        match self.eos.components() {
+            1 => Ok(arr1(&[0.0])),
+            _ => Ok(self.ln_phi() - &self.ln_phi_pure()?),
+        }
+    }
+
     /// Partial derivative of the logarithm of the fugacity coefficient w.r.t. temperature: $\left(\frac{\partial\ln\varphi_i}{\partial T}\right)_{p,N_i}$
     pub fn dln_phi_dt(&self) -> QuantityArray1<U> {
         let func = |s: &Self, evaluate: Evaluate| {