The most common cause for gas in the oil is a broken piston ring. A bad valve seal can also cause the problem.
They are all gas.
I get 19-21 mpg in mine i have a 2002 ext. cab w/4.3 vortec
About 15mpg
According to the 1998 Ford Escort Owner Guide : All models have a ( 48.5 liter / 12.8 U.S. gallon gas tank )
89 OCTANE
It is located on the frame just forward of the gas tank.
4.3 liter vortex motor holds 18 gal.
The gas tank sizes for a 1998 Ford Windstar are : GL with the 3.0 liter V6 engine ( 20.0 U.S. gallons ) GL with the 3.8 liter V6 engine ( 20.0 or the optional 25.0 U.S. gallons ) LX (25.0 U.S. gallons )
For a 1998 Ford Explorer XLT : The 4.0 liter SOHC , V6 and the 5.0 liter V8 take ( " regular " unleaded , 87 octane )
http://dodgeram.org/tech/gas/specs/5_9v8.htm
A liter is a measure of volume. So a liter of liquid ocupies the same amount of space as a liter of gas.
It is part of the fuel pump module inside the tank.