Does is make sense to wait in line for gas?

I was at Costco the other day and gas was selling for $3.95 a gallon, or about ten cents cheaper than the Exxon across the street. Since I was there, I thought about filling up until I saw the line was at about 8 cars deep. I made an exaggerated expression of disgust and surprise that can best be translated into "whatever". Clearly waiting in line with my wife and two kids really wasn't a viable option.

But on the way home I thought, should I have waited? Is it better to wait in line to save $0.10 a gallon?

Hmm ... A little intellectual restlessness ...

According to the American Society of Mechanical Engineers the average engine uses 0.5 gal while idling for 90 minutes; and 0.5 gal is used every 60 minutes of idle time with the AC on. It was about 95 degrees that day so my AC was crankin ' full blast. (Side note, That means a car with a 20 gallon tank could idle for about 2 and a half days. Interesting. This also means the AC really does use more gas, considerably more ... but i digress - Thanks Brian for everything).

According to the EPA gas pumps cannot exceed a dispense rate of 10 gallons per minute. Assuming a 20 gallon tank, pumping would take about 2 minutes. But I think 5 minutes is a better estimate of total elapsed time from car to car. Getting out of the car, finding your credit card, swiping your credit card, accepting the car wash option - but declining the undercarriage wash, etc. It all takes time.

So, for every 2 cars or 10 minutes of idling time, it costs you about $0.33 cents at today's prices of $4.00 per gallon. But I would have saved much more, $2 dollars ($0.10 x 20 gallons) more, by waiting in line and pumping from the cheaper gas at Costco. These estimates suggest it would take an hour (or about 12 cars in line) to make up the difference in gas prices. A workable crude rule of thumb ... every car in line is worth a little less than 1 penny in gas price. So, if the line is about 5 cars deep, you better be getting at least 5 cents off in gas prices. So I guess my impatience got the better of me and I was wrong to pass up the cheaper gas.

But alas ... shouldn't I factor the value of my time into equation? That question will be pondered in a later post.