Gotham Extra Narrow Bold  Suggested by jerseygirl 
Salvo Sans ExtraCond Bold  Suggested by Baki the Builder 
Super Grotesk Condensed Medium  Suggested by donshottype 
Open Sans Condensed Bold  Suggested by donshottype 

This would have been a custom creation.
Influenced by Fututa, with the result being similar to Super Grotesk, developed by Arno Drescher for the Typoart foundry as a substitute for Futura in East Germany after WW II.
FF Super Grotesk Pro Condensed Medium is almost a match.

This one is similar!
Modify M!

Not only the M. Without any need for further checking, also the A.

similar

The logo lettering was created in 1937 or earlier. See 1937 Imperial Oil - Road Map of Eastern Canada http://www.flickriver.com/photos/jeremyhopkin/3021825928/.
It was used as a stand-alone logo until about 1947. See 1947 Imperial - Ontario Road Map http://www.flickriver.com/photos/jeremyhopkin/4448347799/
It was then replaced with an Esso logo that included the old Imperial logo as a sub-text. See 1949 Imperial Esso - Ontario road map http://www.flickriver.com/photos/jeremyhopkin/4455007762/

A true match for the Imperial logo would have to be a font designed before 1937.
As I mentioned in my first post, I believe this was custom lettering influenced by Futura.

Edited
Imperial also used a wider width in regular and bold, which are somewhat similar.

probably nothing around that is a free font hey? Not wanting to spend that much for a font just for one word...
Thanks so much for the help so far!

EDITED
Free fonts that match your sign are as scarce as hen's teeth.
Google has Open Sans Condensed Bold that would work as a substitute except for the _M_, which could be edited by cutting out the middle portion of the width, moving the lhs and rhs sections together and doing some tweeking of _M_