The classic way to convey the error that exists in a measurement is a formula that shows the obtained measurement (X) as a sum of a true score plus some error. One version of this formula is: X = T + e. With this formula in mind, obtaining more precise measures depends on reducing error.
  Mega is the prefix meaning one million, therefore there are one million (1,000,000) gallons in a mega gallon.
How many gallons in a barrel of oil? There are 55 gallons in a drum and 42 gallons (1 U.S. gallon = 3.78541178 liters) in a barrel (i.e., 1 barrel = 158.9872948 liters). Originally there were 40 gallons to a baâ¦rrel. A little over 19 gallons of gasoline can be refined from a barrel of oil. Other products (jet fuel, lubricants, etc.) make up the rest.