Why is the fuel economy of my Ford S-Max decreasing?

I recently noticed that the fuel economy of my Ford S-Max is not as good as it used to be. I have been maintaining regular maintenance and using fuel-efficient driving techniques, but it doesn't seem to be helping. What could be causing this and what steps can I take to improve it?

One possible reason for the decreasing fuel economy could be a dirty air filter. Make sure to regularly clean or replace it according to your manufacturer's recommendations.

Another factor could be under-inflated tires, which can increase fuel consumption. Check your tire pressure and keep them properly inflated.

If your car is a bit older, it could be due to worn spark plugs. Make sure to get them replaced regularly to maintain optimal fuel efficiency.