diff --git a/dagmc/dagnav.py b/dagmc/dagnav.py
index 4d79bb6..7eb2719 100644
--- a/dagmc/dagnav.py
+++ b/dagmc/dagnav.py
@@ -231,11 +231,13 @@ def id(self) -> int:
     @id.setter
     def id(self, i: int):
         """Set the DAGMC set's ID."""
-        if i in self.model.used_ids[type(self)]:
+        if i is None:
+            i = max(self.model.used_ids[type(self)], default=0) + 1
+        elif i in self.model.used_ids[type(self)]:
             raise ValueError(f'{self.category} ID {i} is already in use in this model.')
-        else:
-            self.model.used_ids[type(self)].discard(self.id)
-            self.model.used_ids[type(self)].add(i)
+
+        self.model.used_ids[type(self)].discard(self.id)
+        self.model.used_ids[type(self)].add(i)
 
         self._tag_set_data(self.model.id_tag, i)
 
@@ -367,7 +369,12 @@ def get_triangle_coordinate_mapping(self, compress=False):
         return tri_map, coords
 
     def delete(self):
-        """Delete this group from the DAGMC file."""
+        """Delete this set from the MOAB database, but doesn't
+        delete this DAGSet object.  The object remains but no
+        longer refers to anything in the model.  In many cases, it may
+        make sense to delete this DAGSet object immediately following
+        this operation."""
+        self.model.used_ids[type(self)].discard(self.id)
         self.model.mb.delete_entity(self.handle)
         self.handle = None
         self.model = None
@@ -381,8 +388,7 @@ def create(cls, model: DAGModel, global_id: Optional[int] = None) -> DAGSet:
         ent_set.category = cls._category
         # Now that the entity set has proper tags, create derived class and return
         out = cls(model, ent_set.handle)
-        if global_id is not None:
-            out.id = global_id
+        out.id = global_id
         return out
 
 
@@ -678,9 +684,6 @@ def create(cls, model: DAGModel, name: Optional[str] = None, group_id: Optional[
         # Now that entity set has proper tags, create Group, assign name, and return
         group = cls(model, ent_set.handle)
 
-        if group_id is None:
-            group_id = max((grp.id for grp in model.groups), default=0) + 1
-
         group.id = group_id
 
         if name is not None:
diff --git a/test/test_basic.py b/test/test_basic.py
index eafb2cb..4b672b2 100644
--- a/test/test_basic.py
+++ b/test/test_basic.py
@@ -185,6 +185,16 @@ def test_id_safety(request):
     v1.id = safe_vol_id
     assert v1.id == safe_vol_id
 
+    v2 = Volume.create(model)
+    assert v2.id == safe_vol_id + 1
+
+    safe_vol_id = 101
+    v1.id = safe_vol_id
+    del v2
+
+    v3 = Volume.create(model)
+    assert v3.id == safe_vol_id + 1
+
     s1 = model.surfaces_by_id[1]
 
     used_surf_id = 2
@@ -195,6 +205,13 @@ def test_id_safety(request):
     s1.id = safe_surf_id
     assert s1.id == safe_surf_id
 
+    s2 = model.surfaces_by_id[2]
+    s2.id = None
+    assert s2.id == safe_surf_id + 1
+
+    s2.id = 2
+    assert s2.id == 2
+
     g1 = model.groups_by_name['mat:fuel']
 
     used_grp_id = 2