All pressure cylinders in North America used for liquefied petroleum gases (LPG) must meet the standards set by the Compressed Gas Association (CGA), regardless of whether they are made of steel or aluminum. However, there is anecdotal evidence from accidents that suggests that an aluminum propane cylinder is much more likely to fail than a steel one when exposed to fire in an accident. In order to test and quantify this, a series of fire tests were performed on standard 33.5 lb (DOT 4E240) propane cylinders. Three aluminum cylinders and three steel cylinders were tested under three different fire conditions, covering a range of fire engulfment severity. In all cases, the cylinders were horizontal and the fire was directed onto the side and top of the cylinders. In matching tests, all 3 aluminum cylinders failed in less than 10 minutes, including one boiling liquid expanding vapor explosion (BLEVE), while all 3 steel cylinders did not fail even after more than 40 minutes in the fire. This paper presents the results and an analysis of the fire test data.