What you have is a round version of the G&B 33-C. It dates from around 1915 and to correct something Thunder said above, it was not originally used to fill oil bottles. Oil bottles, as shown above, were not invented until 1922. Prior to that time, most oil was dispensed into a metal can, mostly cans with a spout.
The information I have on the 33-C does not state what size tanks were available with that pump, but I have never heard of a 33 gallon tank. Most tanks were either 35 or 65 gallon tanks.
At the time your tank was made, G&B was partially owned by the Standard Oil Co. G&B made many items with a Standard logo on them. Your unit was possibly made for them.
Jack Sim