Demand would be entirely weather dependent as well.
And, of course, since Global Warming is an assumed fact,
the demand should be less every year.
It cycles with weather, but not entirely weather dependent. Propane is also used in several industrial processes, making Propylene and Polypropylene for example.
In 1999, 19.6 billion gallons of propane were consumed in the U.S. as follows:
• 8 billion gallons for residential/commercial/recreational usage.
• 0.4 billion gallons for internal combustion engine usage.
• 9.8 billion gallons for chemical, industrial and utility usage.
• 1.4 billion gallons for other uses, including such agricultural applications as grain drying and flame cultivation.