diff --git a/environment.yml b/environment.yml
index 449f573..bb61905 100644
--- a/environment.yml
+++ b/environment.yml
@@ -8,7 +8,7 @@ dependencies:
   - graphviz  # used only in chapter 6 for dot files
   - python-graphviz  # used only in chapter 6 for dot files
   - ipython=8.5  # a powerful Python shell
-  - ipywidgets=8.0  # optionally used only in chapter 11 for tqdm in Jupyter
+  - ipywidgets=8.0  # optionally used only in chapter 12 for tqdm in Jupyter
   - joblib=1.1  # used only in chapter 2 to save/load Scikit-Learn models
   - jupyterlab=3.4  # to edit and run Jupyter notebooks
   - matplotlib=3.5  # beautiful plots. See tutorial tools_matplotlib.ipynb
@@ -28,7 +28,7 @@ dependencies:
   - scikit-learn=1.1  # machine learning library
   - scipy=1.9  # scientific/technical computing library
   - statsmodels=0.13  # used only in chapter 15 for time series analysis
-  - tqdm=4.64  # a progress bar library
+  - tqdm=4.64  # used only in chapter 12 to display nice progress bars
   - wheel  # built-package format for pip
   - widgetsnbextension=4.0  # interactive HTML widgets for Jupyter notebooks
   - pip:
@@ -42,6 +42,6 @@ dependencies:
     - tensorflow~=2.10.0  # Deep Learning library
     - transformers~=4.21.3  # Natural Language Processing lib for TF or PyTorch
     - urlextract~=1.6.0  # optionally used in chapter 3, exercise 4
-    - gym[atari,accept-rom-license]~=0.21.0  # used only in chapter 18
+    - gym[atari,accept-rom-license]~=0.26.1  # used only in chapter 18
     - google-cloud-aiplatform~=1.17.0  # used only in chapter 19
     - google-cloud-storage~=2.5.0  # used only in chapter 19
diff --git a/requirements.txt b/requirements.txt
index 0afdbfe..7fd1c4f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -46,7 +46,7 @@ tensorflow-addons~=0.17.1
 
 # There are a few dependencies you need to install first, check out:
 # https://github.com/openai/gym#installing-everything
-gym[Box2D,atari,accept-rom-license]~=0.21.0
+gym[Box2D,atari,accept-rom-license]~=0.26.1
 
 # WARNING: on Windows, installing Box2D this way requires:
 # * Swig: http://www.swig.org/download.html