diff --git a/.kokoro/python3.6/common.cfg b/.kokoro/python3.6/common.cfg
index 64461dc1587..b8f73b97551 100644
--- a/.kokoro/python3.6/common.cfg
+++ b/.kokoro/python3.6/common.cfg
@@ -51,6 +51,12 @@ env_vars: {
     value: "python-docs-samples-tests-py36"
 }
 
+# Number of test workers.
+env_vars: {
+    key: "NUM_TEST_WORKERS"
+    value: "10"
+}
+
 env_vars: {
     key: "TRAMPOLINE_DOCKERFILE"
     value: ".kokoro/docker/Dockerfile"
diff --git a/.kokoro/python3.7/common.cfg b/.kokoro/python3.7/common.cfg
index 372695b38ed..7b5b311d365 100644
--- a/.kokoro/python3.7/common.cfg
+++ b/.kokoro/python3.7/common.cfg
@@ -51,6 +51,12 @@ env_vars: {
     value: "python-docs-samples-tests-py37"
 }
 
+# Number of test workers.
+env_vars: {
+    key: "NUM_TEST_WORKERS"
+    value: "10"
+}
+
 env_vars: {
     key: "TRAMPOLINE_DOCKERFILE"
     value: ".kokoro/docker/Dockerfile"
diff --git a/.kokoro/python3.8/common.cfg b/.kokoro/python3.8/common.cfg
index 90340e9dfb6..b57cc273daf 100644
--- a/.kokoro/python3.8/common.cfg
+++ b/.kokoro/python3.8/common.cfg
@@ -51,6 +51,12 @@ env_vars: {
     value: "python-docs-samples-tests-py38"
 }
 
+# Number of test workers.
+env_vars: {
+    key: "NUM_TEST_WORKERS"
+    value: "10"
+}
+
 env_vars: {
     key: "TRAMPOLINE_DOCKERFILE"
     value: ".kokoro/docker/Dockerfile"
diff --git a/.kokoro/tests/run_tests.sh b/.kokoro/tests/run_tests.sh
index 5c10a877aac..9baf011ce80 100755
--- a/.kokoro/tests/run_tests.sh
+++ b/.kokoro/tests/run_tests.sh
@@ -51,6 +51,19 @@ if [[ $* == *--only-diff-head* ]]; then
     fi
 fi
 
+# Because Kokoro runs presubmit builds simalteneously, we often see
+# quota related errors. I think we can avoid this by changing the
+# order of tests to execute (e.g. reverse order for py-3.8
+# build). Currently there's no easy way to do that with btlr, so we
+# temporarily wait few minutes to avoid quota issue for py-3.8
+# presubmit build.
+if [[ "${RUN_TESTS_SESSION}" == "py-3.8" ]] \
+       && [[ "${KOKORO_JOB_NAME}" == *presubmit ]]; then
+    echo -n "Detected py-3.8 presubmit build,"
+    echo "Wait few minutes to avoid quota issues."
+    sleep 5m
+fi
+
 if [[ -z "${PROJECT_ROOT:-}" ]]; then
     PROJECT_ROOT="github/python-docs-samples"
 fi
@@ -108,10 +121,15 @@ test_prog="${PROJECT_ROOT}/.kokoro/tests/run_single_test.sh"
 btlr_args=(
     "run"
     "**/requirements.txt"
-    "--max-concurrency"
-    "30"
 )
 
+if [[ -n "${NUM_TEST_WORKERS:-}" ]]; then
+    btlr_args+=(
+	"--max-concurrency"
+	"${NUM_TEST_WORKERS}"
+    )
+fi
+
 if [[ -n "${DIFF_FROM:-}"  ]]; then
     btlr_args+=(
 	"--git-diff"