From 1930:

DRM (Reefer) ?

RPX (Tank) Shell Petroleum (St. Louis, Mo)

StLBM (Box) ? SLMB was St. Louis Merchants Bridge Terminal Railway

SKYX (Tank) Skelly Oil Company (Tulsa, Oklahoma)

UPRX (Tank) ? VPRX was Vickers Petroleum (Wichita, Kansas). UPPX was United
Producers Pipe Lines Company (Tulsa, Oklahoma)

WEOX (Tank) ? WECX was Western Equipment Company (Chicago, Illinois).

Regards,

Guy Wilber
Earthquake Faults, Nevada