diff --git a/evofr/posterior/posterior_handler.py b/evofr/posterior/posterior_handler.py
index 6a7bb7b..b55779d 100644
--- a/evofr/posterior/posterior_handler.py
+++ b/evofr/posterior/posterior_handler.py
@@ -1,10 +1,80 @@
 import json
+import pickle
 from typing import Dict, List, Optional
 
 from evofr.data.data_spec import DataSpec
 from evofr.posterior.posterior_helpers import EvofrEncoder
 
 
+def determine_method(filepath):
+    """
+    Determines the serialization method based on the file extension.
+
+    Parameters:
+        filepath (str): The path of the file including its extension.
+
+    Returns:
+        str: The serialization method ("json" or "pickle").
+
+    Raises:
+        ValueError: If the file extension is not recognized.
+    """
+    import os
+
+    _, ext = os.path.splitext(filepath)
+    if ext.lower() == ".json":
+        return "json"
+    elif ext.lower() == ".pkl":
+        return "pickle"
+    return None
+
+
+def save_data(data, filename, method="json"):
+    """
+    Save data to a file using either JSON or pickle based on the user's choice.
+
+    Parameters:
+    - data: The data to be serialized and saved.
+    - filename: The filename where the data will be saved.
+    - method: The serialization method ('json' or 'pickle').
+
+    Raises:
+    - ValueError: If the provided method is not supported.
+    """
+    if method == "json":
+        with open(filename, "w") as file:
+            json.dump(data, file, cls=EvofrEncoder)
+    elif method == "pickle":
+        with open(filename, "wb") as file:
+            pickle.dump(data, file)
+    else:
+        raise ValueError("Unsupported serialization method. Use 'json' or 'pickle'.")
+
+
+def load_data(filename, method="json"):
+    """
+    Load data from a file using either JSON or pickle based on the user's choice.
+
+    Parameters:
+    - filename: The filename from which the data will be loaded.
+    - method: The serialization method ('json' or 'pickle').
+
+    Returns:
+    - The data loaded from the file.
+
+    Raises:
+    - ValueError: If the provided method is not supported.
+    """
+    if method == "json":
+        with open(filename, "r") as file:
+            return json.load(file)
+    elif method == "pickle":
+        with open(filename, "rb") as file:
+            return pickle.load(file)
+    else:
+        raise ValueError("Unsupported deserialization method. Use 'json' or 'pickle'.")
+
+
 class PosteriorHandler:
     def __init__(
         self,
@@ -30,16 +100,27 @@ def __init__(
         self.data = data
         self.name = name
 
-    def save_posterior(self, filepath: str):
+    def save_posterior(self, filepath: str, method=None):
+        if method is None:
+            method = determine_method(filepath)
+            assert (
+                method is not None
+            ), """Serialization method could not be determined from `filepath`. 
+                Please define explicitly or use compatiable file extension e.g. .json or .pkl)"""
+
         """Save posterior samples at a given filepath."""
-        if self.samples is not None:
-            with open(filepath, "w") as file:
-                json.dump(self.samples, file, cls=EvofrEncoder)
+        save_data(self.samples, filepath, method=method)
 
-    def load_posterior(self, filepath: str):
+    def load_posterior(self, filepath: str, method=None):
         """Load posterior samples from a given filepath."""
-        with open(filepath, "w") as file:
-            self.samples = json.load(file)
+        if method is None:
+            method = determine_method(filepath)
+            assert (
+                method is not None
+            ), """Serialization method could not be determined from `filepath`. 
+                Please define explicitly or use compatiable file extension e.g. .json or .pkl)"""
+        self.samples = load_data(filepath, method=method)
+        return self
 
     def unpack_posterior(self):
         """Return samples and dataspec from PosteriorHandler."""