How much gasoline is being transported in the US at any given time?

kranky

Elite Member
Oct 9, 1999
21,019
156
106
We're considering asking this question in job interviews just to get a feel for how someone thinks. Many questions like this are on the net and we're getting canned responses, so we want to use a question which wasn't familiar. Before we decide I thought I'd ask ATOT to collectively think through the question because the group is a lot smarter than I am.

To save you all from Googling, accept these as fact...
- The US consumes 400 million gallons of gasoline per day.
- A tanker truck can hold 9,000 gallons of gasoline.
- There are about 130,000 gas stations in the US
- The average gas station can store 20,000 gallons of gas in their underground tanks.
- The average US household consumes 4 gallons of gas per day.

The question would be: at any given time, how much gasoline is being transported? (IOW, not sitting motionless in a storage tank or refining facility.)

How would you try to come up with a ballpark number? There's no right or wrong, it's not a math problem, and you can make all the assumptions you want if they make sense.
 

FoBoT

No Lifer
Apr 30, 2001
63,084
14
81
fobot.com
are you including pipelines? maybe there are no gas pipelines, i guess i was thinking of oil
trains probably transport from refineries to local depots
are you focusing on "in transit to retail locations, ie gas stations"?
 

DaveSimmons

Elite Member
Aug 12, 2001
40,730
670
126
I'd say "trick question, the tankers bring in oil to be refined into gasoline" :)

Edit: d'oh! I read that as transported into the US -- need more coffee :eek:

Assuming I was awake for the interview, I'd say the average is the 400 million but it would actually go up and down within some range with an upper bound of 9,000 * the number of tankers in service.
 

maxster

Banned
Sep 19, 2007
628
0
0
Well, the answer is simple. The average gasoline being transported per hour is the amount consumed per day/ 24 h.

Think about it a bit and you'll see.
 

ElFenix

Elite Member
Super Moderator
Mar 20, 2000
102,380
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150 million cars on the road.

lets say they average 20 gallon tanks, and on average those tanks are half full. so 10x150 million gallons being transported in cars.
 

JulesMaximus

No Lifer
Jul 3, 2003
74,542
921
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What kind of positions are these people interviewing for? Seems like kind of an off the wall question to me. I'd probably wonder what the hell this has to do with the position I'm applying for.
 

maxster

Banned
Sep 19, 2007
628
0
0
Originally posted by: ElFenix
150 million cars on the road.

lets say they average 20 gallon tanks, and on average those tanks are half full. so 10x150 million gallons being transported in cars.

Hahah. I didn't even think of that as transporting the gas but I guess technically you're right, even though I believe the spirit of the question is otherwise.
 

OutHouse

Lifer
Jun 5, 2000
36,410
616
126
Originally posted by: ElFenix
150 million cars on the road.

lets say they average 20 gallon tanks, and on average those tanks are half full. so 10x150 million gallons being transported in cars.

yea thats what i first thought about. based on the number of cars i would say nearly all gas in in the country is being transported.
 

sygyzy

Lifer
Oct 21, 2000
14,001
4
76
This is a bad interview question. I am not sure if you've read the Mt. Fuji book but the one I like to ask is "How many gas stations are there in the country." The reason is it's possible/easy for the average person to think aloud and figure this out even if they have no idea what the answer is. The average person knows or can figure out things like how many citizens there are, who rarely or does not drive (minors, elderly), how long a session lasts (they've filled up before right?), how many mpg a car gets, hours in a day, etc.
 

QED

Diamond Member
Dec 16, 2005
3,428
3
0
Going on those assumptions:

400,000,000 gallons of gas used daily / 4 gallons of gas used per household = 100,000,000 households.

100,000,000 households / 130,000 gas stations = 739 households serviced per gas station

739 households * 4 gallons of gas daily = 3076 gallons of gas sold daily by average gas station

Assuming every gas station wants to keep their storage tanks filled, they will have a single tanker deliver
a load of gas (9,000 gallons) every 3 days.

Hence, on any given day 130,000 / 3 = 43,333 gas stations will have a single tanker deliver gas to them on that day.

Each tanker holds 9,000 gallons, so 43,333 * 9,000 = 389,999,700 gallons of gas transported daily. This is essentially
the same 400,000,000 gallons that is consumed daily.

What this is showing (all rounding errors aside) is that Maxster was right: the average amount of gas being transported at any moment should be
the average amount of gas being consumed-- if we assume that the amount of gas being stored at each gas station is to remain constant.

So how much of this 400,000,000 gallons delivered daily is actually on the road at any given time during that day? If T is the average driving time
of a tanker from where it gets filled up to where it empties itself at a gas station (measured in minutes), then the average amount of gas on the road
at any given time should be 400,000,000 * T / 60 / 24.
 

kranky

Elite Member
Oct 9, 1999
21,019
156
106
Very interesting answers. As I said in the OP, it's not all that important to us what the precise answer is, it's about hearing how someone would analyze the problem.

Whether or not you count how much is in the tanks of vehicles on the road doesn't matter because either way it's choosing to make a reasonable assumption for the purpose of going through the rest of the problem.

We've tried this out on some of our engineers giving them the list of facts in the OP, and the answers have been all over the place but the interesting part was seeing how people used some or all of those facts to work out an answer. Some included gas in the individual vehicles on the road, some did not.

Any other approaches out there?