Hi doc ---

here's some things that may give you a better idea of the 'how' -

In 2015, refineries in the United States produced an average of about 19 gallons of motor gasoline
and 12 gallons of ultra-low sulfur distillate fuel oil (includes diesel fuel and heating oil)
from one * 42-gallon barrel * of crude oil. - - - Note- NOT a 55gal bbl, as many think.

Many other petroleum products are also refined from crude oil.

The name "refining" is used in the sense of converting something rough/dirty/crude into something pure and useful.
So it's not really about reduction.
It's hard to answer this question as written, because refining is mostly about separation --
1 gallon of crude only makes about 0.4-0.5 gallons of gasoline,
but at the same time it also makes 0.3 gallons of diesel,
0.1 gallons of jet fuel,
and a bunch of other stuff that actually adds up to about 1.05 gallons of product.
On a volume basis, you get more out than you put in.

So there is no one number for how much gasoline you'll get from a single barrel or gallon of oil.
You would have to know what oil you're starting with, which refinery is refining it,
and what the optimal production ratios are for the current market prices of the various products.

Here's a US refinery product breakdown:

http://www.txoga.org/articles/30...

the ' how ' also linked below --

http://pascagoula.chevron.com/abouttherefinery/whatwedo/processingandrefining.aspx

.- r