I recently acquired a small lot of commercial first-day covers prepared by the Texas Refinery Corporation (not Texaco). The earliest I have is 1960 and the latest I have seen was 1964. A scan of one is below.

I believe the Texas Refinery Corp sold various lubricants by using field salesmen. These covers apparently were sent to the corporation's officers, selected employees, and field salesmen.
Does any know who was behind these covers? Was it simply the corporation's marketing department, or was there a specific collector in marketing, or a corporation officer who was a collector who promoted the covers?
How early did these covers begin and how long did their issuance continue? Is there a checklist of them?
Thanks
Don