One theory says that as the companies have developed better refining methods to improve the yield of gasoline from a barrel of crude, the amount of diesel and fuel oil per barrel has of course decreased. Then stricter exhaust emissions rules required a lower sulfur content in the fuel, which in turn requires additional refining steps and increases costs for the oil company. So at the same time that much of the industry in this country abandoned rail in favor of trucks (to support just-in-time delivery and reduced inventories), the supply of diesel was reduced and the cost to produce it increased. Increased demand with reduced supply equals higher prices.
JMHO - Jerry
While I was in Guatemala, I looked into purchasing a new 4 door diesel truck to leave down there with the boat. I could purchase a Chinese made 4 door truck that looked identical to a Ford Ranger....with an Isuzu diesel motor, 5 speed trans, 4 wheel drive, and loaded with all the electric door locks and windows ets....for under $12,000 american. The diesel fuel down there is less refined but cost $4.00 a gallon. All the fuel there is shipped in, so that is why fuel is soo expensive. Some of their imported fuel is from Venezuela where diesel is under $0.20 a gallon.
Inquired about having this truck shipped into the USA.....$5000 shipping.....$8000 to upgrade the motor to meet the emissions for the USA. Fuel economy before changes is 45-50 mpg....after 20-25 mpg.
They also had a Chinese made motorcycle that looked like a cross between a V-Star and a Harley Fatboy....$2500 american, and gets over 70 mpg.
Don't know about some...but making my own bio-diesel is becoming more favorable.