diff --git a/pypsa_validation_processing/statistics_functions.py b/pypsa_validation_processing/statistics_functions.py
index 007cfe3..70fc6cf 100644
--- a/pypsa_validation_processing/statistics_functions.py
+++ b/pypsa_validation_processing/statistics_functions.py
@@ -87,24 +87,19 @@ def Final_Energy_by_Sector__Transportation(
 
     Notes
     -----
-    The actual extraction of transportation final energy from the network
-    collection will be implemented by the user.  A typical call would be::
-
-        network_collection.statistics.energy_balance(
-            comps=["Load"], carrier="transport"
-        )
-
-    The current implementation returns a dummy value of ``0.0 MWh`` for the
-    year 2020 so that the end-to-end workflow can be tested.
+    Includes all transportation-relevant carriers for component Load. Vehicle to Grid
+    does not need to be evaluated, as evaluation is restricted to Load-Components only.
     """
     # sum over all transportation-relevant sectors - 2 different units involved.
-    result = (
+    res = (
         n.statistics.energy_balance(
             carrier=[
                 "land transport EV",
                 "land transport fuel cell",
+                "land transport oil",
                 "kerosene for aviation",
                 "shipping methanol",
+                "shipping oil",
             ],
             components="Load",
             groupby=["carrier", "unit", "country"],
@@ -113,4 +108,4 @@ def Final_Energy_by_Sector__Transportation(
         .groupby(["country", "unit"])
         .sum()
     )
-    return result
+    return res
diff --git a/tests/test_statistics_functions.py b/tests/test_statistics_functions.py
index bf16c45..89f5803 100644
--- a/tests/test_statistics_functions.py
+++ b/tests/test_statistics_functions.py
@@ -21,16 +21,16 @@
 class TestFinalEnergyByCarrierElectricity:
     """Test suite for Final_Energy_by_Carrier__Electricity function."""
 
-    def test_returns_dataframe(self, mock_network: MockPyPSANetwork):
-        """Test that the function returns a pandas DataFrame or Series."""
+    def test_returns_series(self, mock_network: MockPyPSANetwork):
+        """Test that the function returns a pandas Series."""
         result = Final_Energy_by_Carrier__Electricity(mock_network)
-        assert isinstance(result, (pd.DataFrame, pd.Series))
+        assert isinstance(result, pd.Series)
 
-    def test_has_country_and_unit_index(self, mock_network: MockPyPSANetwork):
-        """Test that result has country and unit in the index."""
+    def test_has_country_and_unit_multiindex(self, mock_network: MockPyPSANetwork):
+        """Test that result has MultiIndex with country and unit levels."""
         result = Final_Energy_by_Carrier__Electricity(mock_network)
-        assert "country" in result.index.names
-        assert "unit" in result.index.names
+        assert isinstance(result.index, pd.MultiIndex)
+        assert result.index.names == ["country", "unit"]
 
     def test_not_empty(self, mock_network: MockPyPSANetwork):
         """Test that result is not empty."""
@@ -53,7 +53,9 @@ def test_multiple_networks(self, mock_network_collection: MockNetworkCollection)
         """Test processing multiple networks from collection."""
         for network in mock_network_collection:
             result = Final_Energy_by_Carrier__Electricity(network)
-            assert isinstance(result, (pd.DataFrame, pd.Series))
+            assert isinstance(result, pd.Series)
+            assert isinstance(result.index, pd.MultiIndex)
+            assert result.index.names == ["country", "unit"]
             assert len(result) > 0
 
 
@@ -65,16 +67,16 @@ def test_multiple_networks(self, mock_network_collection: MockNetworkCollection)
 class TestFinalEnergyBySectorTransportation:
     """Test suite for Final_Energy_by_Sector__Transportation function."""
 
-    def test_returns_dataframe(self, mock_network: MockPyPSANetwork):
-        """Test that the function returns a pandas DataFrame or Series."""
+    def test_returns_series(self, mock_network: MockPyPSANetwork):
+        """Test that the function returns a pandas Series."""
         result = Final_Energy_by_Sector__Transportation(mock_network)
-        assert isinstance(result, (pd.DataFrame, pd.Series))
+        assert isinstance(result, pd.Series)
 
-    def test_has_country_and_unit_index(self, mock_network: MockPyPSANetwork):
-        """Test that result has country and unit in the index."""
+    def test_has_country_and_unit_multiindex(self, mock_network: MockPyPSANetwork):
+        """Test that result has MultiIndex with country and unit levels."""
         result = Final_Energy_by_Sector__Transportation(mock_network)
-        assert "country" in result.index.names
-        assert "unit" in result.index.names
+        assert isinstance(result.index, pd.MultiIndex)
+        assert result.index.names == ["country", "unit"]
 
     def test_not_empty(self, mock_network: MockPyPSANetwork):
         """Test that result is not empty."""
@@ -97,5 +99,7 @@ def test_multiple_networks(self, mock_network_collection: MockNetworkCollection)
         """Test processing multiple networks from collection."""
         for network in mock_network_collection:
             result = Final_Energy_by_Sector__Transportation(network)
-            assert isinstance(result, (pd.DataFrame, pd.Series))
+            assert isinstance(result, pd.Series)
+            assert isinstance(result.index, pd.MultiIndex)
+            assert result.index.names == ["country", "unit"]
             assert len(result) > 0