diff --git a/tox.ini b/tox.ini
index eb1014fda..8af7581a7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -24,6 +24,7 @@ deps =
 commands = stestr run {posargs}
 
 [testenv:pep8]
+basepython = python3
 commands =
   {toxinidir}/tools/run-bashate.sh
   flake8 {posargs} kayobe
@@ -33,13 +34,16 @@ commands =
   {toxinidir}/tools/sphinx8 README.rst CONTRIBUTING.rst doc/source --ignore D001
 
 [testenv:venv]
+basepython = python3
 deps =
-    -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/pike}
+    -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/queens}
     -r{toxinidir}/test-requirements.txt
     -r{toxinidir}/doc/requirements.txt
 commands = {posargs}
 
 [testenv:ansible]
+# Kolla currently fails during password generation under python3. Revisit in Rocky.
+basepython = python2
 usedevelop = True
 # Create the virtualenv with access to system site packages, as this is
 # required to use the python and apt modules, which are not available via PyPI.
@@ -52,6 +56,8 @@ commands =
     {toxinidir}/tools/test-ansible.sh {posargs}
 
 [testenv:molecule]
+# Molecule only supports python 2.7 and 3.6.
+basepython = python2
 whitelist_externals =
     bash
     sudo
@@ -67,9 +73,11 @@ commands =
     sudo bash -c "source {envdir}/bin/activate && {toxinidir}/tools/test-molecule.sh {posargs}"
 
 [testenv:alint]
+basepython = python3
 commands = ansible-lint ansible/*.yaml
 
 [testenv:ansible-syntax]
+basepython = python3
 commands =
     # Install ansible role dependencies from Galaxy.
     ansible-galaxy install \
@@ -90,6 +98,7 @@ commands =
         {posargs}"
 
 [testenv:cover]
+basepython = python3
 setenv =
     VIRTUAL_ENV={envdir}
     PYTHON=coverage run --source kayobe --parallel-mode
@@ -102,6 +111,7 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
+basepython = python3
 deps =
     -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/queens}
     -r{toxinidir}/requirements.txt
@@ -109,11 +119,13 @@ deps =
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [testenv:releasenotes]
+basepython = python3
 deps =
-    -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/pike}
+    -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/queens}
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/doc/requirements.txt
 commands =