diff --git a/Dockerfile b/Dockerfile
index e8f8e06..1688963 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -11,8 +11,11 @@ RUN pip install --no-cache-dir -r requirements.txt
 # Copy application code
 COPY app/ .
 
-# Expose port
-EXPOSE 5000
+# Set default port environment variable
+ENV PORT=5000
 
-# Start command
-CMD ["python", "app.py"]
+# Expose port (optional for documentation)
+EXPOSE ${PORT}
+
+# Start command using shell to allow env substitution
+CMD ["sh", "-c", "exec python app.py --port=${PORT}"]
diff --git a/app/app.py b/app/app.py
index b1e67fe..5e29965 100644
--- a/app/app.py
+++ b/app/app.py
@@ -64,4 +64,5 @@ def index():
     )
 
 if __name__ == "__main__":
-    app.run(debug=(FLASK_ENV == "development"), host="0.0.0.0", port=5000)
+    port = int(os.getenv("PORT", 5000))
+    app.run(debug=(FLASK_ENV == "development"), host="0.0.0.0", port=port)
diff --git a/docker-compose.yml b/docker-compose.yml
index 46586f6..d6a00b4 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -1,3 +1,5 @@
+version: '3.8'
+
 services:
   portfolio:
     build:
@@ -6,7 +8,9 @@ services:
     image: application-portfolio
     container_name: portfolio
     ports:
-      - "5000:5000"
+      - "${PORT:-5000}:5000"
     volumes:
       - ./app:/app
+    environment:
+      - PORT=${PORT:-5000}
     restart: unless-stopped
diff --git a/env.example b/env.example
new file mode 100644
index 0000000..3c34789
--- /dev/null
+++ b/env.example
@@ -0,0 +1,2 @@
+PORT=5000
+FLASK_ENV=production
\ No newline at end of file
diff --git a/main.py b/main.py
index a95e8e6..c839547 100755
--- a/main.py
+++ b/main.py
@@ -22,6 +22,7 @@ import argparse
 import subprocess
 import sys
 import os
+PORT = int(os.getenv("PORT", 5000))
 
 def run_command(command, dry_run=False):
     """Utility function to run a shell command."""
@@ -94,7 +95,7 @@ def run_dev(args):
     volume_mapping = f"{current_dir}/app/:/app"
     command = [
         "docker", "run", "-d",
-        "-p", "5000:5000",
+        "-p", f"{PORT}:{PORT}",
         "--name", "portfolio",
         "-v", volume_mapping,
         "-e", "FLASK_APP=app.py",
@@ -115,7 +116,7 @@ def run_prod(args):
     """
     command = [
         "docker", "run", "-d",
-        "-p", "5000:5000",
+        "-p", "{PORT}:{PORT}",
         "--name", "portfolio",
         "application-portfolio"
     ]