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.
There are approximately 358 U.S. gallons per metric ton. According to conversion tables at the Iowa State University website, 1 United States gallon is equal to 0.002791 metric tons. Conversely, there are 1/0.002791 gallons per metric ton, which works out to 358.294518 U.S. gallons per metric ton.