This is the earliest known logo, from the company's website.
This logo followed with the removal of the "SINCO" brand and its replacement with more symbolic imagery of the company's business. The corporate colors of green and red were added here for the first time.
Here the logo was further simplified to reflect the primary business of gasoline sales. The green color was also lightened.
This is the first logo to feature the pentagonal shield outline and the company's advertising mascot, an apatosaur nicknamed "Dino." The company still uses this logo today.