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.
I believe it is supposed to have a fuel tank capacity of 19.8 US Gallons. The most gasoline that we have been able to pump in is 18.4 US Gallons. This was going slow for the last 1-2 gallons. and pulling the gas pump handle up a little. I am not sure if all 2007-2009 Santa Fe's use the 19.8 US Gallon fuel tank. It does look like the 2010 Santa Fe uses. the 19.8 US gallon fuel tank and then the 2011 Santa Fe reduced the fuel tank to 18 US Gallons (I think).