Why can't I find the top tier gas logo at these stations? Exxon, Mobil and Shell are all(00)

Why can't I find the top tier gas logo at these stations? Exxon, Mobil and Shell are all(00)

Image gallery: Is Exxon Top Tier Gas

Why can't I find the top tier gas logo at these stations? Exxon, Mobil and Shell are all Top Tier Gas Logo Not All Gas is Created Equal: Here’s What You Need to Know – CareDoctor