diff --git a/game/monsters.py b/game/monsters.py
index 96b98a8..2ba8ea6 100644
--- a/game/monsters.py
+++ b/game/monsters.py
@@ -57,7 +57,32 @@ def spawn(self, x: int, y: int) -> Actor:
 ]
 
 
-def eligible_monsters(depth: int) -> list[MonsterType]:
-    min_level = max(1, min(depth - 5, len(monsters) - 4))
-    max_level = max(5, min(depth + 4, len(monsters)))
-    return [m for m in monsters[min_level - 1:max_level] if m.generate]
+def get_monster_types(depth: int) -> tuple[list[MonsterType], list[int]]:
+    items = []
+    weights = []
+    for i, weight in enumerate(_weights(depth)):
+        if weight > 0 and monsters[i].generate:
+            items.append(monsters[i])
+            weights.append(weight)
+    return items, weights
+
+
+def _weights(depth: int) -> list[int]:
+    assert depth >= 1
+    weights = [0] * 26
+    under = 0
+    over = 0
+    for i in range(depth - 6, depth + 4):
+        if i < 0:
+            under += 10
+        elif i >= len(weights):
+            over += 10
+        else:
+            weights[i] += 10
+    for i in range(0, 5):
+        weights[i] += under // 5
+    for i in range(21, 26):
+        weights[i] += over // 5
+    assert len(weights) == 26
+    assert sum(weights) == 100
+    return weights
diff --git a/game/procgen.py b/game/procgen.py
index 3ee0146..c36a728 100644
--- a/game/procgen.py
+++ b/game/procgen.py
@@ -7,7 +7,7 @@
 from game.entity import ArmorItem, Item, WeaponItem
 from game.items import get_item_categories
 from game.level import Level
-from game.monsters import eligible_monsters
+from game.monsters import get_monster_types
 
 # hardcoded 80x22 subdivision
 H_GRID = [0, 26, 27, 53, 54, 80]
@@ -247,8 +247,9 @@ def place_gold(room: Room, level: Level) -> None:
 
 def place_monster(room: Room, level: Level) -> None:
     x, y = find_empty_spot_in_room(room, level)
-    m_type = rng.choice(eligible_monsters(level.depth))
-    monster = m_type.spawn(x, y)
+    monster_types, weights = get_monster_types(level.depth)
+    monster_type = rng.choices(monster_types, weights).pop()
+    monster = monster_type.spawn(x, y)
     level.entities.add(monster)
 
 
diff --git a/tests/test_monsters_weights.py b/tests/test_monsters_weights.py
new file mode 100644
index 0000000..1fa323b
--- /dev/null
+++ b/tests/test_monsters_weights.py
@@ -0,0 +1,66 @@
+import pytest
+
+import game.monsters
+
+
+@pytest.mark.skip(reason="Enable to dump the full table.")
+def test_dump_weights():
+    print()
+    for d in range(1, 33):
+        weights = game.monsters._weights(d)
+        print("  ".join(f"{item:2d}" for item in weights))
+
+
+def test_level_1():
+    weights = game.monsters._weights(1)
+    assert weights == [20] * 5 + [0] * 21
+
+
+def test_level_2_to_5():
+    for d in range(2, 6):
+        weights = game.monsters._weights(d)
+        assert weights == [22 - 2 * d] * 5 + [10] * (d - 1) + [0] * (22 - d)
+
+
+def test_level_6():
+    weights = game.monsters._weights(6)
+    assert weights == [10] * 10 + [0] * 16
+
+
+def test_level_7_to_21():
+    for d in range(7, 22):
+        weights = game.monsters._weights(d)
+        assert weights == [0] * (d - 6) + [10] * 10 + [0] * (22 - d)
+
+
+def test_level_22():
+    weights = game.monsters._weights(22)
+    assert weights == [0] * 16 + [10] * 10
+
+
+def test_level_23_to_26():
+    for d in range(23, 27):
+        weights = game.monsters._weights(d)
+        assert weights == [0] * (d - 6) + [10] * (27 - d) + [2 * d - 34] * 5
+
+
+def test_level_27():
+    weights = game.monsters._weights(27)
+    assert weights == [0] * 21 + [20] * 5
+
+
+def test_level_28_to_31():
+    for d in range(28, 32):
+        weights = game.monsters._weights(d)
+        assert weights == [0] * 21 + [2 * d - 44] * (d - 27) + [2 * d - 34] * (32 - d)
+
+
+def test_level_32():
+    weights = game.monsters._weights(32)
+    assert weights == [0] * 21 + [20] * 5
+
+
+def test_level_33_and_beyond():
+    for d in range(33, 100):
+        weights = game.monsters._weights(d)
+        assert weights == [0] * 21 + [20] * 5