It is 1931, it's been raining, the unpaved roads are a quagmire of mud, and this guy needs some gas, so he pulls into the local Indian Gas Station to fill up on the latest in new gasoline technology, Texaco's Ethyl.
Indian Refining had been a major player in the gasoline and oil markets since 1902, but on January 14, 1931 the Texas Corporation gained controlling interest in Indian and soon began infiltrating its branding. Texas, under their Texaco brand, had introduced Ethyl gasoline in late 1930, and the acquisition of the Indian stations gave Texas a new outlet in the Midwest to sell this new and improved gasoline formula. It is rebranded "Texaco Fire Chief" in April 1932, so there was only a relatively small window when this photo could have been taken.
Ethyl, by the way, is the snazzy branding of the lead in leaded gasoline (technically, it is tetraethyl lead, or TEL). We have Unleaded gasoline today because of the rather nasty cumulative effects of lead building up in the environment. But they didn't know such things back then.